Intron analyses reveal multiple calmodulin copies in Littorina

Intron three and the flanking exons of the calmodulin gene have been amplified, cloned and sequenced from 18 members of the gastropod genus Littorina. From the 48 sequences, at least five different gene copies have been identified and their functionality characterized using a strategy based upon the potential protein product predicted from flanking exon data. The functionality analyses suggest that four of the genes code for functional copies of calmodulin. All five copies have been identified across a wide range of littorinid species although not ubiquitously. Using this novel approach based on intron sequences, we have identified an unprecedented number of potential calmodulin copies in Littorina, exceeding that reported for any other invertebrate. This suggests a higher number of, and more ancient, gene duplications than previously detected in a single genus

On Primordial Sense–Antisense Coding

The genetic code is implemented by aminoacyl-tRNA synthetases (aaRS). These twenty enzymes are divided into two classes that, despite performing same functions, have nothing common in structure. The mystery of this striking partition of aaRSs might have been concealed in their sterically complementary modes of tRNA recognition that, as we have found recently, protect the tRNAs with complementary anticodons from confusion in translation. This finding implies that, in the beginning, life increased its coding repertoire by the pairs of complementary codons (rather than one-by-one) and used both complementary strands of genes as templates for translation. The class I and class II aaRSs may represent one of the most important examples of such primordial sence-antisence (SAS) coding (Rodin and Ohno, 1995). In this report, we address the issue of SAS coding in a wider scope. We suggest a variety of advantages that such coding would have had in exploring a wider sequence space before translation became highly specific. In particular, we confirm that in Achylia klebsiana a single gene might have originally coded for an HSP70 chaperonin (class II aaRS homolog) and an NAD-specific GDH-like enzyme (class I aaRS homolog) via its sense and antisense strands. Thus, in contrast to the conclusions in (Williams et al., 2009), this could indeed be a “Rosetta stone” (eroded somewhat, though) gene for the SAS origin of the two aaRS classes (Carter and Duax, 2002)