Mammalian reovirus L3 gene sequences and evidence for a distinct amino-terminal region of the λ1 protein

To complement evidence for nucleoside triphosphate phosphohydrolase (NTPase), RNA helicase, RNA 5' triphosphate phosphohydrolase, and nucleic acid-binding activities by the core shell protein lambda 1 of mammalian orthoreoviruses (reoviruses), we determined nucleotide sequences of the lambda 1-encoding L3 gene segments from three isolates: type 1 Lang (T1L), type 2 Jones (T2J), and type 3 Dearing (T3D). The T1L and T3D L3 gene sequences and deduced Al protein sequences shared high levels of identity (97.7% and 99.3%, respectively). The lambda 1 sequences differed at only 9 of 1275 amino acids. Two single-nucleotide insertions relative to a previously published sequence for T3D L3 extended the Al open reading frame to within 60 nucleotides of the plus-strand 3' end for T3D and the other isolates sequenced, in keeping with the short 3' nontranslated regions of the other nine gene segments. Seven of the nine amino acid differences between T1L and T3D lambda 1 were located within the amino-terminal 500 residues of Al, a region with putative sequence similarities to NTPases and RNA helicases. The T2J L3 and lambda 1 sequences were found to be more divergent especially within the amino-terminal 180 residues of hi, preceding the putative CCHH zinc finger motif. The T2J L3 sequence, along with partial sequences for L3 genes from three other reovirus isolates, suggested that one or more of the polymorphisms at amino acids 71, 215, 500, 1011, and/or 1100 in Al contribute to the L3-determined differences in ATPase activities by T1L and T3D cores. The findings contribute to our ongoing efforts to elucidate sequence-structure-function relationships for the Al core protein. (C) 1999 Academic Press.