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contraction, and then compiled a nonredundant list of mammalian genes in these and all children categories and checked whether these genes were detected in PP1 our data set. We excluded from the analysis eleven genes not pres ent in the mouse heart EST library and detected 129 of the 135 remaining cardiac muscle related genes in our dataset, Of the 8,533 UniGenes with assigned gene symbols known to be expressed in the mouse heart, 7,970 of these symbols are present in the ENSEMBL collection of mouse genes. We detected 7,129 of them in our sequences, which indicated that representation of genes expressed in the heart, regardless of their expression levels, was almost complete in our study. This conclusion holds even if we consider all mouse UniGenes, including those with no gene symbol assigned.
such UniGenes represent poorly characterized, often weakly expressed transcripts. Blast searches of the bank vole sequences against the entire mouse UniGene database detected 79. 9% of the 10,963 UniGenes with expression reported in the heart. On the other hand, sequences PP1 similar to 15,630 mouse UniGenes not known to be expressed in the mouse heart were detected, indi cating that the expression information in public data bases may be very incomplete. Because two steps of our cDNA preparation procedure involved PCR amplification, a possible bias against detec tion of long transcripts might have occurred. To evaluate this possibility, we compared the length distribution of transcripts in all mouse ENSEMBL genes with the length distribution of transcripts of genes detected in the bank vole.
Contrary to the expecta tion, we found that genes with short transcripts were underrepresented RGFP966 in our experiments, the relative fre quencies of genes with transcripts 1 2 kb long were almost identical in ENSEMBL mouse gene collection, and genes with longer transcripts were actually overrepre sented in our dataset, Protein biosynthesis Thus, no bias against the detection of longer transcripts was introduced by our amplification procedures. Another, perhaps more informative, measure of tran scriptome completeness is the fraction of the transcript length covered by the bank vole sequences.
As the refer ence we used the data Combretastatin A-4 on the transcript length and loca tion of coding sequences from the ECMT, Nearly full transcript length was obtained PP1 for 960 transcripts, and for many more an almost complete CDS was identified, As could have been expected there was a negative correlation between the mouse tran script length and the fraction of transcript covered by the bank vole sequences, although this effect was rather weak, The mean fraction covered was 0. 387, Notably, the coding regions of transcripts had a much higher frac tion of their length covered than 3 and 5 UTRs, There are at least two alternative explanations for the lower 3 and 5 UTR coverage. It is possible Combretastatin A-4 that a bias was introduced during laboratory sequencing procedures, causing under representation of cDNA ends both in the primary 454 library and, consequently, in the obtained sequences. On the other hand, under representation of UTRs may reflect weaker evolutionary conservation of these regions, resulting in a lack of sequence similarity to mouse transcripts over a sub stantial portion of contig singleton length.
Thus, artifactual under representation of these regions would be caused by sequence divergence in the UTRs beyond the PP1 point of blast detectable similarity and not by the actual bias against UTRs in our sequences. We evaluated these two explanations by analyzing CS mapping to those mouse transcripts that contained the protein coding regions. Assuming that each CS indeed represented a continuous cDNA stretch, for each CS we computed the proportion of its length that did not have significant simi larity to the mouse transcript, separately for the parts fall ing into 5UTR, CDS and 3UTR. The proportion was much higher Combretastatin A-4 in 5 UTRs and 3UTRs than in CDS, Thus, weaker evolutionary conservation of untranslated transcript reg