Frequently asked questions¶
Can MView extract BLAST (or other) output into a FASTA/PIR/MSF/CLUSTAL file?¶
Yes - MView extracts and converts results into FASTA, PIR, MSF and CLUSTAL/aln formats. See Output formats.
Can MView extract or view the separate BLAST alignment or HSPs?¶
Yes - MView normally displays or extracts only the top scoring alignments or
HSPs for the query. You can get all alignments and/or HSPs using the
Does MView work with nucleotide sequences?¶
Yes - use one of the
-moltype rna or
options to tell MView to use an appropriate colour scheme for HTML output
(currently, these three options are equivalent).
Can MView use CLUSTAL colours?¶
Yes - use the
-colormap CLUSTAL option to change the colourmaps for
both protein and nucleotide alignments.
Can MView process data from a Web page?¶
Basically, no, unless you are lucky or prepared to edit the Web page. The MView parsers are all built to recognise the raw text output produced by the respective programs (BLAST, FASTA, etc.) or to recognise particular flat-file formats (MSF, PIR, etc.). When a site adds HTML markup to this to make a Web page, arbitrary parts are changed/deleted/added polluting the text, so that even dumping the page in text-only format still leaves traces.
Can I switch off HTML markup?¶
Yes - the program defaults to plain text output unless the
-html option is
set to any valid value other than
off, or the output format is set to PIR,
MSF, FASTA, or RDB.
How can I print?¶
From the web browser. To produce something that fits on typical paper sizes
one must set
-width 60 or similar and turn off some of the leading text,
Can I edit the alignment?¶
No - MView isn’t an alignment editor. You could try to copy/paste the output into a spreadsheet and process it there, then reload it into MView.
What do the percent identities mean?¶
By default, percent identities reported in each alignment row are calculated with respect to the aligned portion of the reference sequence (usually the query or first row) thus:
Still, in the case of BLAST MView output, minor deviations from the
percentages reported by BLAST are due to (1) different rounding, and (2) the
way MView assembles a single pseudo-sequence (see Why are some symbols lowercased?)
for a hit composed of multiple HSPs, giving an averaged percent identity. This
default behaviour above is also obtained using the option
Two other calculation possibilities are available:
normalises by the ungapped length of the query or reference sequence, and
-pcid hit normalises by the ungapped length of the hit sequence.
You can change the reference sequence against which identities are calculated
-reference option, which requires either a row number or a
Why are some symbols lowercased?¶
Gapped input (e.g., FASTA, BLAST2, PSI-BLAST) is subject to a further processing step when producing the stacked alignment. The query sequence acts as a template, but any gaps introduced into the query by a database hit are excised to ensure a contiguous query string. The position of the excision in the affected hit is marked by lowercasing the pair of boundary symbols.
Why is the query sequence incomplete?¶
The displayed query sequence is assembled from the input data, not by reference to any external sequence database. MView will pad missing query sequence with ‘X’ characters based on the numeric match ranges if this is needed to complete an assembly. Occasionally, you may see a ‘?’ character - this means that a non-standard residue was seen on input.
How are overlapping BLAST HSPs processed?¶
Ungapped BLAST input is processed to produce a stack of hit sequence strings aligned against a contiguous query sequence. The query sequence acts as a template for each hit sequence onto which hit fragments are overlayed in the query positions.
In outline the default method of processing of HSPs is as follows:
For BLAST (series 1), as of MView version 1.37, only the HSPs contributing to the ranked hit contribute to this overlay process. A sorting scheme ensures that the best of these fragments are overlayed last and are not obscured by weaker ones, for example, BLAST hits are sorted by score and length. Differences of ordering of fragments along query and hit naturally result in a patchwork that may not correspond exactly to the real hit sequences. Nevertheless, the resulting alignment stack is very informative, and the user can always run and view a gapped search if that is preferred.
For BLAST (series 2) and PSI-BLAST, often only a single gapped alignment is reported by blast for a given database hit. However, sometimes there are alternative alignments and the same stacking rules apply.
Greater control over the choice of HSPs is available through the
option. See BLAST HSP processing rules for more details.