In vitro functional analysis of a temperature-sensitive mutant of vesicular stomatitis virus, New Jersey serotype, defective in transcription

The fates of undermethylated mRNA cap structures of vesicular stomatitis virus (New Jersey) during in vitro transcription

A dual label pulse-chase analysis employing S-adenosyl-L-[methyl-3H]methionine and [beta-32P]GTP has been devised to identify precursors to the cap structure 7mG(5')ppp(5')Am present on the 5'-termini of vesicular stomatitis virus mRNAs. Both monomethylated cap structures, 7mG(5')ppp(5')A and G(5')ppp(5')Am, have been detected in vitro in New Jersey serotype reactions containing suboptimal concentrations of S-adenosyl-L-methionine. The simultaneous chasing of both radiolabeled substrates allowed the determination of the transcriptive fate of each pulse-labeled cap structure in the total RNA population. Ten percent of the 7mG(5')ppp(5')A cap structure and 27% of the G(5')ppp(5')Am cap structure generated during the pulse were chased into 7mG(5')ppp(5')Am. These results suggested that while there may have been a preferred order of 5'-cap methylation, the order was not compulsory. The dual label analysis also revealed that only 34% of the pulse-labeled G(5')ppp(5')A cap structure could be chased into methylated cap structures. A nascent RNA chain length-dependent "methylation window" is proposed.

Assignment of the temperature-sensitive lesion in the replication mutant A1 of vesicular stomatitis virus to the N gene

The replication defect in the temperature-sensitive mutant A1 of the New Jersey serotype (Hazelhurst subtype) of vesicular stomatitis virus was confirmed by the absence of intracellular nucleocapsids in infected cells incubated at the restrictive temperature. After preamplification, the relative yield of the A1 N protein accumulated intracellularly after 1 h of incubation at the restrictive temperature was decreased by 50% that of the wild-type or revertant A1 N protein. This difference was not as apparent in pulse-chase experiments. The functional lesion in A1 was correlated with a structural alteration in the N protein on the basis of the thermolability of the template activity of the A1 N protein-RNA complex in in vitro transcription reactions and the covariance of this phenotype with the temperature-sensitive phenotype in a spontaneous A1 revertant. This correlation was consistent with a direct role of the N protein in replication and allowed the assignment of the N gene to complementation group A.

Structural and functional characterization of the RNA-positive complementation groups, C and D, of the New Jersey serotype of vesicular stomatitis virus: assignment of the M gene to the C complementation group

The structural and functional lesions in the RNA-positive complementation groups, C and D, of the New Jersey serotype (Hazelhurst subtype) of vesicular stomatitis virus have been characterized. The M protein of the temperature-sensitive mutant C1, the prototype of the C complementation group, was degraded at the restrictive temperature in vivo, and was resolved from the wild-type M protein by SDS-polyacrylamide gel electrophoresis and nonequilibrium pH gradient electrophoresis. Coreversion of these properties and the temperature-sensitive phenotype was observed in a spontaneous revertant. On the basis of these results, the M gene was assigned to the C complementation group. Intracellular nucleocapsids could not be isolated from New Jersey serotype infections by procedures developed for Indiana serotype infections. Therefore, in order to assess the ability of New Jersey ts mutants to accumulate nucleocapsids at the restrictive temperature, a procedure for their isolation was developed. Hypertranscription was observed in C1-infected cells incubated at the restrictive temperature, but was not accompanied by proportionate increases in intracellular viral nucleocapsids or protein synthesis. The G and N proteins of the temperature-sensitive mutant D1, the sole representative of the D complementation group, were electrophoretic variants. The relative yield of intracellular D1 N protein was lower at the restrictive than at the permissive temperature, and the D1 L protein was thermolabile. No intracellular viral nucleocapsids were detected in D1 infected cells incubated at the restrictive temperature; however, more 40 S and less message-sized RNA were synthesized at the restrictive than at the permissive temperature. These results suggested functional defects in both the N protein and polymerase of D1.