Rift Valley fever virus L segment: correction of the sequence and possible functional role of newly identified regions conserved in RNA-dependent polymerases.

The sequence of Rift Valley fever virus L segment that we published in a previous paper was erroneous in the 3'-terminal region of the antigenomic RNA molecule. Here, we have shown that the L segment is in fact 6404 nucleotides long and encodes a polypeptide of 237.7K in the viral complementary sense. Sequence comparisons performed between the RNA-dependent RNA polymerases of 22 negative-stranded RNA viruses revealed the existence of two novel regions located at the amino termini of the proteins and conserved only in the polymerases of bunya- and arenaviruses. In the region conserved in all RNA-dependent polymerases, corresponding to the so-called 'polymerase module', we identified a new motif, designated premotif A, common to all RNA-dependent polymerases, as well as amino acids located in the region between motifs preA and A which are strictly conserved for segmented negative-stranded RNA viruses. Using the recently released coordinates of human immunodeficiency virus reverse transcriptase and the alignment between all RNA-dependent polymerases in the 'polymerase module', we have determined the position of the conserved residues in these polymerases and discuss their possible functions in light of the available structural information.