2ndscore — find the best hairpin anchored at each position.
2ndscore in.fasta > out.hairpins
For every position in the sequence this will output a line:
-0.6 52 .. 62 TTCCTAAAGGTTCCA GCG CAAAA TGC CATAAGCACCACATT
(score) (start .. end) (left context) (hairpin) (right contenxt)
For positions near the ends of the sequences, the context may be padded
with 'x' characters. If no hairpin can be found, the score will be
Multiple fasta files can be given and multiple sequences can be in each
fasta file. The output for each sequence will be separated by a line
starting with '>' and containing the FASTA description of the sequence.
Because the hairpin scores of the plus-strand and minus-strand may
differ (due to GU binding in RNA), by default 2ndscore outputs two sets
of hairpins for every sequence: the FORWARD hairpins and the REVERSE
hairpins. All the forward hairpins are output first, and are identified
by having the word 'FORWARD' at the end of the '>' line preceding them.
Similarly, the REVERSE hairpins are listed after a '>' line ending with
'REVERSE'. If you want to search only one or the other strand, you can
--no-fwd Don't print the FORWARD hairpins
--no-rvs Don't print the REVERSE hairpins
You can set the energy function used, just as with transterm with the
--gc, --au, --gu, --mm, --gap options. The --min-loop, --max-loop, and
--max-len options are also supported.
FORMAT OF THE .BAG FILES
The columns for the .bag files are, in order:
7. terminator_confidence: a combination of the hairpin and tail score that
takes into account how likely such scores are in a random sequence. This
is the main "score" for the terminator and is computed as described in
8. APPROXIMATE_distance_from_end_of_gene: The *approximate* number of base
pairs between the end of the gene and the start of the terminator. This
is approximate in several ways: First, (and most important) TransTermHP
doesn't always use the real gene ends. Depending on the options you give
it may trim some off the ends of genes to handle terminators that
partially overlap with genes. Second, where the terminator "begins"
isn't that well defined. This field is intended only for a sanity check
(terminators reported to be the best near the ends of genes shouldn't be
_too far_ from the end of the gene).
USING TRANSTERM WITHOUT GENOME ANNOTATIONS
TransTermHP uses known gene information for only 3 things: (1) tagging
the putative terminators as either "inside genes" or "intergenic," (2)
choosing the background GC-content percentage to compute the scores,
because genes often have different GC content than the intergenic
regions, and (3) producing slightly more readable output. Items (1) and
(3) are not really necessary, and (2) has no effect if your genes have
about the same GC-content as your intergenic regions.
Unfortunately, TransTermHP doesn't yet have a simple option to run
without an annotation file (either .ptt or .coords), and requires at
least 2 genes to be present. The solution is to create fake, small
genes that flank each chromosome. To do this, make a fake.coords file
that contains only these two lines:
fakegene1 1 2 chome_id
fakegene2 L-1 L chrom_id
where L is the length of the input sequence and L-1 is 1 less than the
length of the input sequence. "chrom_id" should be the word directly
following the ">" in the .fasta file containing your sequence. (If, for
example, your .fasta file began with ">seq1", then chrom_id = seq1).
This creates a "fake" annotation with two 1-base-long genes flanking
the sequence in a tail-to-tail arrangement: --> <--. TransTermHP can
then be run with:
transterm -p expterm.dat sequence.fasta fake.coords
If the G/C content of your intergenic regions is about the same as your
genes, then this won't have too much of an effect on the scores
terminators receive. On the other hand, this use of TransTermHP hasn't
been tested much at all, so it's hard to vouch for its accuracy.
Alex Mestiashvili <email@example.com>