[Characteristic of the two-step RNA dimerization in avian sarcoma and leukosis viruses].

Dimerization of two copies of genomic RNA is a necessary step of retroviral replication. In the case of human immunodeficiency virus type 1 (HIV-1) the process is explored in many details. It is proved that conserved stem-loop structure is an essential element in RNA dimerization. Similar model of two-step dimerization mechanism can be considered for avian sarcoma and leukosis virus group (ASLV) in spite of the absence of homology between dimer initiation site (DIS) of ASLV and that of HIV-1. In this paper, short RNA fragments of two viruses: avian sarcoma virus CT-10 and avian leukosis virus HPRS-103 have been chosen in order to investigate the structural requirements of dimerization process and compare them to that of HIV-1. The rate of spontaneous transition from loose to tight dimer was studied as a function of stem length and temperature. Although both types of dimers were observed for both avian retroviruses chosen, fragments of CT-10 requires much higher RNA concentration to form loose dimer. In spite of identical sequence of the loops (5'-A-CUGCAG-3') avian sarcoma virus CT-10 RNA fragments dimerization was greatly impaired. The differences can be explained by deletion of adenine 271 in avian sarcoma virus CT-10 in the stem and by resulting shortening of the self-complementary loop.