[Location of the reconstitution initiation sites of TMV Ni2519 RNA].

The nature of temperature sensitivity (ts) of TMV mutant Ni2529 has been studied in experiments on in vitro reconstitution. At permissive temperature (24 degrees C) RNA of Ni2519 can be reassembled into an infective virus. At nonpermissive temperature (33 degrees C) the reassembly of Ni2519 results in defective (ribonuclease-sensitive) particle formation. The RNase-sensitive site of Ni2519 RNA molecule in the defective virus particle is located at a distance of about 600--800 nucleotides from the 3'-end. The reason for the aberrant Ni 2519 reconstitution at 33 degrees C is that initiation of reassembly at nonpermissive temperature occurs simultaneously at two reconstitution initiation sites of Ni2519 RNA. The first site (RISI) is located within about 800--1000 nucleotides from 3'-terminus and corresponds to the origin of assembly region of TMV common strain. The second site (RISII) is located within about 300--520 nucleotides from 3'-terminus and corresponds to the portion of coat protein gene. The RNA site available for RNase attack is located just between the two RIS. Thus, it has been suggested that the ts-phenotype of Ni2519 results from ts-behaviour of the virion RNA molecule itself, i. e. that this mutant represents novel class of TMV ts-mutants.