VITRO PACKAGING OF INDIVIDUAL GENOMIC SEGMENTS OF BACTERIOPHAGE-PHI-6RNA - SERIAL DEPENDENCE RELATIONSHIPS

Bacteriophage phi 6 has a genome of three segments of double-stranded RNA enclosed in a procapsid composed of four different proteins. The p reformed procapsid is capable of packaging plus-strand transcripts of the genomic segments in an in vitro reaction. The packaging of the thr ee segments shows a strong order of dependence in that segment S packa ges alone, but segment M requires S and segment L requires S and M for efficient packaging. Packaging of individual segments is dependent on unique packaging sequences of about 200 nucleotides near the 5' ends of the segments. Deletions that invade these regions destroy packaging competence for the particular segment and for the dependent segments as well. In the presence of 2 mM phosphate and at magnesium ion concen trations above 4 mM, packaging becomes progressively more independent and ultimately nonspecific with respect to phi 6 sequences.