Completion of the Tula hantavirus genome sequence: properties of the L segment and heterogeneity found in the 3' termini of S and L genome RNAs.

In this study the L segment and the 5' and 3' termini of the S, M and L segments of the prototype Tula hantavirus (TUL) were sequenced, thus completing the first determination of the genome sequence of a hantavirus that has not been linked to any human disease. The TUL L segment comprises 6541 nt with one ORF of 6459 nt in the antigenome sense. This ORF potentially encodes a 2153 aa protein with a predicted molecular mass of 247 kDa. The amino acid sequence includes all the motifs conserved in RNA-dependent RNA polymerases. The 5' termini of all three genome RNAs (vRNAs) had the expected sequences conserved in hantaviruses. The 3' termini of M vRNAs were also conserved. However, the 3' termini of S and L vRNAs were heterogeneous as most of the sequenced 3' termini had either deletions of 1 to 22 nt or an extra 1 to 3 nt. No increase in the level of heterogeneity was seen in vRNAs of virions collected 3, 6, 9 and 12 days post-infection, suggesting that the heterogeneity already exists at the early stages of infection. The S and L vRNAs from infected cells had more truncated 3' termini than vRNAs from pelleted virus. Heterogeneity of the 3' termini of genome RNAs could decrease the efficiency of antigenome and mRNA syntheses and contribute to the slow growth observed for TUL and other hantaviruses in cell culture.