Coat protein binding sites on RNA 1 of alfalfa mosaic virus.

The largest genome segment, RNA 1, of alfalfa mosaic virus forms complexes with viral coat protein. These complexes were subjected to digestion with ribonucleases T1 or A and filtered onto Millipore filters. Specific fragments were collected from the filters by phenol extraction. After electrophoretic separation in denaturing polyacrylamide gels, these fragments were sequenced. Besides extracistronic fragments originating from the 3'-terminal region of RNA 1, fragments were found originating from an intracistronic region of the RNA. A striking phenomenon is that the intracistronic fragments were not found when ribonuclease A was used to degrade RNA/protein complexes. The findings are in agreement with the postulation of Houwing and Jaspars (1978), that a conformational change at the 3' ends of the genome RNAs induced by the coat protein is a prerequisite to start an infection cycle.