DIMERIZATION OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 RNA INVOLVES SEQUENCES LOCATED UPSTREAM OF THE SPLICE DONOR SITE

The retroviral genome consists of two homologous RNA molecules associa ted close to their 5' ends. We studied the spontaneous dimerization of four HIV-1 RNA fragments (RNAs 1-707, 1-615, 311-612, and 311-415) co ntaining the previously defined dimerization domain, and a RNA fragmen t (RNA 1-311) corresponding to the upstream sequences. Significant dim erization of all RNAs is observed on agarose gels when magnesium is in cluded in the electrophoresis buffer. In contrast to dimerization of R NAs 311-612 and 311-415, dimerization of RNAs 1-707, 1-615 and 1-311 s trongly depends on the size of the monovalent cation present in the in cubation buffer. Also, dimerization of RNAs 1-707, 1-615, and 1-311 is 10 times faster than that of RNAs 311-612 and 311-415. The dimers for med by the latter RNAs are substantially more stable than that of RNA 1-615, while RNA 1-311 dimer is 5-7 degrees C less stable than RNA 1-6 15 dimer. These results indicate that dimerization of HIV-1 genomic RN A involves elements located upstream of the splice donor site (positio n 305), i.e. outside of the previously defined dimerization domain.