Location of the cistron of the tobacco mosaic virus coat protein.

Treatment of tobacco mosaic virus (TMV) RNA with T1 RNase under mild conditions cuts the RNA molecule into a large number of fragments, only a few of which may be specifically recognized by disks of TMV protein. It has been shown elsewhere that these specifically recognized RNA fragments are a part of the coat protein cistron, the portion coding for amino acids 95 to 129 of the coat protein. It is reported that different size classes of partially uncoated virus particles were prepared by limited reconstitution between TMV RNA and protein or by partial stripping of intact virus with DMSO. Both procedures produce nucleoprotein rods in which the 5'-terminal portion of the RNA is encapsidated and the 3'-terminal region is free. The free and the encapsidated portions of the RNA were each tested for the ability to give rise to the aforesaid specifically recognized fragments of the coat protein cistron upon partial T1 RNase digestion. It was found that only the 3'-terminal third of the virus particle need to be uncoated in order to expose the portion of the RNA molecule from which these fragments are derived. We conclude, therefore, that the coat protein cistron is situated upon the 3'-terminal third of the RNA chain, i.e. within 2000 nucleotides of the 3'-end.