ClustalW help for version 1.4 (September 1994).




This is the on-line help file for CLUSTAL W.

It should be named or defined as: clustalw_help
except with MSDOS in which case it should be named CLUSTALW.HLP

For full details of usage and algorithms, please see the files:
cluustalv.doc The documentation for Clustal V (most of the program usage
and the basic algorithms are the same).
clustalw.ms A manuscript describing the main algorithmic changes over
Clustal V.
readme.txt A brief summary of the main changes over Clustal V.


Toby Gibson
Des Higgins (now at the EBI, Hinxton, Great Britain)
Julie Thompson

EMBL, Heidelberg, Germany.


The paper describing Clustal W is:

Thompson, J.D., Higgins, D.G. and Gibson, T.J. (1994)
CLUSTAL W: improving the sensitivity of progressive multiple
sequence alignment through sequence weighting, position specific
gap penalties and weight matrix choice.
Nucleic Acids Research, submitted, June 1994.


>>HELP 1 << General help for CLUSTAL W

Clustal W is a general purpose multiple alignment program for DNA or proteins.

SEQUENCE INPUT: all sequences must be in 1 file, one after another.
6 formats are automatically recognised: NBRF/PIR, EMBL/SWISSPROT,
Pearson (Fasta), Clustal (*.aln), GCG/MSF (Pileup) and GDE.
All non-alphabetic characters (spaces, digits, punctuation marks) are ignored
except "-" which is used to indicate a GAP ("." in GCG/MSF).


To do a MULTIPLE ALIGNMENT on a set of sequences, use item 1 from this menu to
INPUT them; go to menu item 2 to do the multiple alignment.

PROFILE ALIGNMENTS (menu item 3) are used to align 2 alignments or to add a set
of new sequences to an old alignment. Use this to add new sequences to an old
alignment. GAPS in the old alignments are
indicated using the "-" character. PROFILES can be input in ANY of the
allowed formats; just use "-" (or "." for MSF) for each gap position.

PHYLOGENETIC TREES (menu item 4) can be calculated from old alignments (read in
with "-" characters to indicate gaps) OR after a multiple alignment while the
alignment is still in memory.


The program tries to automatically recognise the different file formats used
and to guess whether the sequences are amino acid or nucleotide. This is not
always foolproof.

FASTA and NBRF/PIR formats are recognised by having a ">" as the first
character in the file.

EMBL/Swiss Prot formats are recognised by the letters
ID at the start of the file (the token for the entry name field).

CLUSTAL format is recognised by the word CLUSTAL at the beginning of the file.

GCG/MSF format is recognised by the word PileUp at the start of the file. If
your msf files do not contain this word first, edit it in at the start
of the first line.

If 85% or more of the characters in the sequence are from A,C,G,T,U or N, the
sequence will be assumed to be nucleotide. This works in 97.3% of cases
but watch out!




The paper describing Clustal W is:

Thompson, J.D., Higgins, D.G. and Gibson, T.J. (1994)
CLUSTAL W: improving the sensitivity of progressive multiple
sequence alignment through sequence weighting, position specific
gap penalties and weight matrix choice.
Nucleic Acids Research, submitted, June 1994.



>>HELP 2 << Help for multiple alignments

If you have already loaded sequences, use menu item 1 to do the complete
multiple alignment. You will be prompted for 2 output files: 1 for the
alignment itself; another to store a dendrogram that describes the similarity
of the sequences to each other.

Multiple alignments are carried out in 3 stages (automatically done from menu
item 1 ...Do complete multiple alignments now):

1) all sequences are compared to each other (pairwise alignments);

2) a dendrogram (like a phylogenetic tree) is constructed, describing the
approximate groupings of the sequences by similarity (stored in a file).

3) the final multiple alignment is carried out, using the dendrogram as a guide.


PAIRWISE ALIGNMENT parameters control the speed/sensitivity of the initial
alignments.

MULTIPLE ALIGNMENT parameters control the gaps in the final multiple alignments.

RESET GAPS (menu item 7) will remove any new gaps introduced into the sequences
during multiple alignment if you wish to change the parameters and try again.
This only takes effect just before you do a second multiple alignment. You
can make phylogenetic trees after alignment whether or not this is ON.
If you turn this OFF, the new gaps are kept even if you do a second multiple
alignment. This allows you to iterate the alignment gradually. Sometimes, the
alignment is improved by a second or third pass.

SCREEN DISPLAY can be used to send the output alignments to the screen
as well as to the output file.

You can skip the first stages (pairwise alignments; dendrogram) by using an
old dendrogram file (menu item 3); or you can just produce the dendrogram
with no final multiple alignment (menu item 2).

OUTPUT FORMAT: Menu item 9 (format options) allows you to choose from 5
different alignment formats (CLUSTAL, GCG, NBRF/PIR, PHYLIP and GDE).

You can toggle between FAST/APPROXIMATE or SLOW/ACCURATE alignments for
the initial alignments used to make the guide tree. The fast ones are
extremely fast but are less reliable than the slow ones.
>>HELP 3 << Help for pairwise alignment parameters
A distance is calculated between every pair of sequences and these are
used to construct the dendrogram which guides the final multiple alignment.
The scores are calculated from separate pairwise alignments. These can be
calculated using 2 methods: dynamic programming (slow but accurate) or by the
method of Wilbur and Lipman (extremely fast but approximate).

You can choose between the 2 alignment methods using menu option 8. The
slow/accurate method is fine for short sequences but will be VERY SLOW
for many (e.g. >20) long (e.g. >1000 residue) sequences.


SLOW/ACCURATE alignment parameters:

These parameters do not have any affect on the speed of the alignments. They
are used to give initial alignments which are then rescored to give percent
identity scores. These % scores are the ones which are displayed on the
screen. The scores are converted to distances for the trees.

1) Gap Open Penalty: the penalty for opening a gap in the alignment.
2) Gap extension penalty: the penalty for extending a gap by 1 residue.
3) Protein weight matrix: the scoring table which describes the similarity of
each amino acid to each other. For DNA, an identity matrix is used.



FAST/APPROXIMATE alignment parameters:

These similarity scores are calculated from fast, approximate, global align-
ments, which are controlled by 4 parameters. 2 techniques are used to make
these alignments very fast: 1) only exactly matching fragments (k-tuples) are
considered; 2) only the 'best' diagonals (the ones with most k-tuple matches)
are used.


K-TUPLE SIZE: This is the size of exactly matching fragment that is used.
INCREASE for speed (max= 2 for proteins; 4 for DNA), DECREASE for sensitivity.
For longer sequences (e.g. >1000 residues) you may need to increase the default.


GAP PENALTY: This is a penalty for each gap in the fast alignments. It has
little affect on the speed or sensitivity except for extreme values.






TOP DIAGONALS: The number of k-tuple matches on each diagonal (in an imaginary
dot-matrix plot) is calculated. Only the best ones (with most matches) are
used in the alignment. This parameter specifies how many. Decrease for speed;
increase for sensitivity.


WINDOW SIZE: This is the number of diagonals around each of the 'best'
diagonals that will be used. Decrease for speed; increase for sensitivity.


>>HELP 4 << Help for multiple alignment parameters
These parameters control the final multiple alignment. This is the core of
the program and the details are complicated. To fully understand the use
of the parameters and the scoring system, you will have to refer to the
documentation.

Each step in the final multiple alignment consists of aligning two alignments
or sequences. This is done progressively, following the branching order in
the GUIDE TREE. The basic parameters to control this are two gap penalties and
the scores for various identical/non-indentical residues.

1) and 2) The GAP PENALTIES are set by menu items 1 and 2. These control the
cost of opening up every new gap and the cost of every item in a gap.
Increasing the gap opening penalty will make gaps less frequent. Increasing
the gap extension penalty will make gaps shorter. Terminal gaps are not
penalised.

3) The DELAY DIVERGENT SEQUENCES switch delays the alignment of the most
distantly related sequences until after the most closely related sequences have
been aligned. The setting shows the percent identity level required to delay
the addition of a sequence; sequences that are less identical than this level
to any other sequences will be aligned later.



4) For DNA, the scoring system assigns a score of 3 for two identical bases
and zero otherwise. The TOGGLE TRANSITIONS switch (menu item 3) gives
transitions (A <--> G or C <--> T i.e. purine-purine or pyrimidine-pyrimidine
substitutions) a score of 1; otherwise, these are scored as mismatches and
get a score of zero. For distantly related DNA sequences, this switch
might be better turned off; for closely related sequences it can be useful.

5) PROTEIN WEIGHT MATRIX leads to a new menu where you are offered a
choice of weight matrices. The default is the BLOSUM series of
matrices by Jorja and Steven Henikoff. Note, a series is used! The actual
matrix that is used depends on how similar the sequences to be aligned at this
alignment step are. Different matrices work differently at each
evolutionary distance. Further help is offered in the weight matrix menu.

>>HELP A << Help for protein gap parameters.
1) RESIDUE SPECIFIC PENALTIES are amino acid specific gap penalties that reduce
or increase the gap opening penalties at each position in the alignment or
sequence. See the documentation for details. As an example, positions that
are rich in glycine are more likely to have an adjacent gap than positions that
are rich in valine.

2) 3) HYDROPHILIC GAP PENALTIES are used to increase the chances of a gap within
a run (5 or more residues) of hydrophilic amino acids; these are likely to
be loop or random coil regions where gaps are more common. The residues that
are "considered" to be hydrophilic are set by menu item 3.

4) GAP SEPARATION DISTANCE tries to decrease the chances of gaps being
too close to each other. Gaps that are less than this distance apart
are penalised more than other gaps. This does not prevent close gaps;
it makes them less frequent, promoting a block-like appearance of the alignment.

5) END GAP SEPARATION treats end gaps just like internal gaps for the purposes
of avoiding gaps that are too close (set by GAP SEPARATION DISTANCE above).
If this is off (default), end gaps will be ignored for this purpose. This is
useful when you wish to align fragments where the end gaps are not biologically
meaningful.
>>HELP 5 << Help for output format options.
Five output formats are offered. You can choose more than one (or all 5 if
you wish).

CLUSTAL format output is a self explanatory alignment format. It shows the
sequences aligned in blocks. It can be read in again at a later date to
(for example) calculate a phylogenetic tree or add a new sequence with a
profile alignment.

GCG output can be used by any of the GCG programs that can work on multiple
alignments (e.g. PRETTY, PROFILEMAKE, PLOTALIGN). It is the same as the GCG
.msf format files (multiple sequence file); new in version 7 of GCG.

PHYLIP format output can be used for input to the PHYLIP package of Joe
Felsenstein. This is an extremely widely used package for doing every
imaginable form of phylogenetic analysis (MUCH more than the the modest intro-
duction offered by this program).

NBRF/PIR: this is the same as the standard PIR format with ONE ADDITION. Gap
characters "-" are used to indicate the positions of gaps in the multiple
alignment. These files can be re-used as input in any part of clustal that
allows sequences (or alignments or profiles) to be read in.

GDE: this format is used by the GDE package of Steven Smith.


OUTPUT ORDER is used to control the order of the sequences in the output
alignments. By default, it is the same as the input order. This switch can
be used to make the order correspond to the order in which the sequences
were aligned (from the guide tree/dendrogram), thus automatically grouping
closely related sequences.
>>HELP 6 << Help for profile alignments

By PROFILE ALIGNMENT, we mean alignment to an existing alignment. Either of the
alignments can be a single sequence. A profile is simply an alignment of
one or more sequences (e.g. an alignment output file from Clustal W) or a set
of unaligned sequences.

The profiles can be in any of the allowed input formats with "-" characters
used to specify gaps (except for GCG/MSF where "." is used).

You have to specify the 2 profiles by choosing menu items 1 and 2 and giving
2 file names. Then Menu item 3 will align the 2 profiles to each other.

Menu item 4 will take the sequences in the second profile and align them to
the first profile, 1 at a time. This is useful to add some new sequences to
an existing alignment. In this case, the second profile need not be pre-
aligned.

The alignment parameters can be set using menu items 6 and 7 ("Alignment
parameters"). These are EXACTLY the same parameters as used by the general,
automatic multiple alignment procedure. The general multiple alignment proc-
edure is simply a series of profile alignments. Carrying out a series of
profile alignments on larger and larger groups of sequences, allows you to
manually build up a complete alignment.

Profile alignments allow you to store alignments of your favourite sequences
and add new sequences to them in small bunches at a time.
>>HELP 7 << Help for phylogenetic trees
1) Before calculating a tree, you must have an ALIGNMENT in memory. This can be
input in any format or you should have just carried out a full multiple
alignment and the alignment is still in memory. Remember YOU MUST ALIGN THE
SEQUENCES FIRST!!!!

The method used is the NJ (Neighbour Joining) method of Saitou and Nei. First
you calculate distances (percent divergence) between all pairs of sequence from
a multiple alignment; second you apply the NJ method to the distance matrix.

2) EXCLUDE POSITIONS WITH GAPS? With this option, any alignment positions
where ANY of the sequences have a gap will be ignored. This means that 'like'
will be compared to 'like' in all distances. It also, automatically throws
away the most ambiguous parts of the alignment, which are concentrated around
gaps (usually). The disadvantage is that you may throw away much of
the data if there are many gaps.

3) CORRECT FOR MULTIPLE SUBSTITUTIONS? For small divergence (say <10%) this
option makes no difference. For greater divergence, this option corrects
for the fact that observed distances underestimate actual evolutionary dist-
ances. This is because, as sequences diverge, more than one substitution will
happen at many sites. However, you only see one difference when you look at the
present day sequences. Therefore, this option has the effect of stretching
branch lengths in trees (especially long branches). The corrections used here
(for DNA or proteins) are both due to Motoo Kimura. See the documentation for
details. README.TXT describes a new modification for proteins distances.

For VERY divergent sequences, the distances cannot be reliably
corrected. You will be warned if this happens. Even if none of the distances
in a data set exceed the reliable threshold, if you bootstrap the data,
some of the bootstrap distances may randomly exceed the safe limit.


4) To calculate a tree, use option 4 (DRAW TREE NOW). This gives an UNROOTED
tree and all branch lengths. The root of the tree can only be inferred by
using an outgroup (a sequence that you are certain branches at the outside
of the tree .... certain on biological grounds) OR if you assume a degree
of constancy in the 'molecular clock', you can place the root in the 'middle'
of the tree (roughly equidistant from all tips).

5) BOOTSTRAPPING is a method for deriving confidence values for the groupings in
a tree (first adapted for trees by Joe Felsenstein). It involves making N
random samples of sites from the alignment (N should be LARGE, e.g. 500 - 1000);
drawing N trees (1 from each sample) and counting how many times each grouping
from the original tree occurs in the sample trees. You must supply a seed
number for the random number generator. Different runs with the same seed
will give the same answer. See the documentation for details.

6) OUTPUT FORMATS: three different formats are allowed. None of these
displays the tree visually. You must make the tree yourself (on paper)
using the results OR get the PHYLIP package and use the tree drawing facilities
there. (Get the PHYLIP package anyway if you are interested in trees).

>>HELP 8 << Help for choosing protein weight matrix
For protein alignments, you use a weight matrix to determine the similarity of
non-identical amino acids. For example, Tyr aligned with Phe is usually judged
to be 'better' than Tyr aligned with Pro. These are not used with DNA.

There are two 'in-built' series of weight matrices offered. Each consists
of several matrices which work differently at different evolutionary distances.
To see the exact details, read the documentation. Crudely, we store several
matrices in memory, spanning the full range of amino acid distance (from
almost identical sequences to highly divergent ones). For very similar
sequences, it is best to use a strict weight matrix which only gives a high
score to identities and the most favoured conservative substitutions. For
more divergent sequences, it is appropriate to use "softer" matrices which
give a high score to many other frequent substitutions.

1) BLOSUM (Henikoff). These matrices appear to be the best available for
carrying out data base similarity (homology searches). The matrices used are:
Blosum80, 62, 40 and 30.

2) PAM (Dayhoff). These have been extremely widely used since the late '70s.
We use the PAM 120, 160, 250 and 350 matrices.

We also supply an identity matrix which gives a score of 10 to two identical
amino acids and a score of zero otherwise. This matrix is not very useful.
Alternatively, you can read in your own (just one matrix, not a series).

A new matrix can be read from a file on disk, if the filename consists only
of lower case characters. The values in the new weight matrix must be integers
and the scores should be similarities. You can use negative as well as positive
values if you wish, although the matrix will be automatically adjusted to all
positive scores.

INPUT FORMAT The format used for a new matrix is the same as the BLAST program.
Any lines beginning with a # character are assumed to be comments. The first
non-comment line should contain a list of amino acids in any order, using the
1 letter code, followed by a * character. This should be followed by a square
matrix of integer scores, with one row and one column for each amino acid. The
last row and column of the matrix (corresponding to the * character) contain
the minimum score over the whole matrix.
>>HELP 9 << Help for command line parameters
DATA (sequences)

/INFILE=file.ext :input sequences.
/PROFILE1=file.ext and /PROFILE2=file.ext :profiles (old alignment).

VERBS (do things)

/OPTIONS :list the command line parameters
/HELP or /CHECK :outline the command line params.
/ALIGN :do full multiple alignment
/TREE :calculate NJ tree.
/BOOTSTRAP(=n) :bootstrap a NJ tree (n= number of bootstraps; def. = 1000).

PARAMETERS (set things)

***General settings:****
/INTERACTIVE :read command line, then enter normal interactive menus
/QUICKTREE :use FAST algorithm for the alignment guide tree
/NEWTREE= :file for new guide tree
/USETREE= :file for old guide tree
/NEGATIVE :protein alignment with negative values in matrix
/OUTFILE= :sequence alignment file name
/OUTPUT= :GCG, GDE, PHYLIP or PIR
/OUTORDER= :INPUT or ALIGNED
/CASE :LOWER or UPPER (for GDE output only)

***Fast Pairwise Alignments:***
/KTUP=n :word size /TOPDIAGS=n :number of best diags.
/WINDOW=n :window around best diags. /PAIRGAP=n :gap penalty
/SCORE :PERCENT or ABSOLUTE

***Slow Pairwise Alignments:***
/PWMATRIX= :BLOSUM, PAM, ID or filename
/PWGAPOPEN=f :gap opening penalty /PWGAPEXT=f :gap opening penalty

***Multiple Alignments:***
/MATRIX= :BLOSUM, PAM, ID or filename
/GAPOPEN=f :gap opening penalty /GAPEXT=f :gap extension penalty
/ENDGAPS :no end gap separation pen. /GAPDIST=n :gap separation pen. range
/NORGAP :Residue specific gaps off /NOHGAP :hydrophilic gaps off
/HGAPRESIDUES= :list hydrophilic res. /MAXDIV=n :% ident. for delay
/TYPE= :PROTEIN or DNA /TRANSITIONS :transitions NOT weighted.

***Trees:*** /SEED=n :seed number for bootstraps.
/KIMURA :use Kimura's correction. /TOSSGAPS :ignore positions with gaps.

>>HELP 0 << Help for tree output format options

Three output formats are offered: 1) Clustal, 2) Phylip/TreeTool,
3) Just the distances.

None of these formats displays the results graphically. To see a graphic
representation of a tree (not a bootstrapped tree), get the PHYLIP package and
use format 2) below. It can be imported into the PHYLIP programs RETREE,
DRAWTREE and DRAWGRAM and displayed graphically. TreeTool can also do this
but is only available for SUN (by ftp from rdp.life.uiuc.edu). TreeTool,
however has a neat facility for labels on internal nodes which we use to
display bootstrap figures on the bootstrap trees. If you do not have TreeTool,
please request the trees in Clustal format 1) below.


1) Clustal format output.
This format is verbose and lists all of the distances between the sequences
and the number of alignment positions used for each. The tree is described
at the end of the file. It lists the sequences that are joined at each
alignment step and the branch lengths. After two sequences are joined, it is
referred to later as a NODE. The number of a NODE is the number of the
lowest sequence in that NODE.

2) Phylip or TreeTool format output.
This format is the New Hampshire format, used by many phylogenetic analysis
packages. It consists of a series of nested parentheses, describing the
branching order, with the sequence names and branch lengths. With a simple
tree, it can be used by the RETREE, DRAWGRAM and DRAWTREE programs of the PHYLIP
package to see the trees graphically. This is the same format used during
multiple alignment for the guide trees.

With a bootstrap tree, you need to use TreeTool or request format 1) above.

3) The distances only.
This format just outputs a matrix of all the pairwise distances in a format
that can be used by the Phylip package. It used to be useful when one
could not produce distances from protein sequences in the Phylip package but
is now redundant (Protdist of Phylip 3.5 now does this).


Last updated: 8 August 1997.
created by :Fred Opperdoes