LOWER MUTATION-RATE OF BOVINE LEUKEMIA-VIRUS RELATIVE TO THAT OF SPLEEN NECROSIS VIRUS

Genetic variation of the more complex retroviruses in the human T-cell leukemia virus/bovine leukemia virus (HTLV/BLV) group is less than in some other retroviral genera. To test whether reverse transcription o f HTLV/BLV group members is less error prone than that of members of o ther groups, we developed an assay for detecting forward mutations in BLV, similar to that developed for the simpler spleen necrosis virus ( SNV). We used this system to study the rates and types of mutations th at occur during a single replication cycle. We found that BLV reverse transcription is approximately two and one-half times less error prone than SNV reverse transcription (4.8 X 10(-6) versus 1.2 X 10(-5) muta tion per bp per cycle, respectively). The relative numbers of all type s of observed mutations (that is, base pair substitutions, frameshifts , deletions, and deletions with insertions) were similar for BLV and S NV.