Our attention in the past year has focused on the role of the specific tRNAs which are utilized at the A-site within the ribosomal frameshift signal in retroviruses. SRV-1 (simian acquired immunodeficiency virus syndrome [SAIDS]) contains the pro-pol frameshift signal A AAU UUU where phenylalanine tRNA translates the UUU codon at the ribosomal A-site and asparagine tRNA the AAU codon at the ribosomal P-site in the pro reading frame. In SRV-1 infected cells, phenylalanine tRNA was found to lack the highly modified Wye base in its anticodon loop, while asparagine tRNA lacked the highly modified Q base in its anticodon loop. These results further substantiate an earlier observation in correlating tRNA hypomodification and the requirement for the corresponding isoacceptor in translating codons within the ribosomal frameshift signals of HIV, HTLV-1 and BLV. In addition, lysine tRNA4 was elevated in SRV-1 infected cells and this isoacceptor is utilized as primer for the reverse transcriptase. We have also begun a study of the tRNA population included within the HIV virion and have developed an in vivo assay for examining the role of hypomodified tRNAs in ribosomal frameshifting.
