Linear mapping of tryptophan residues in Vesiculovirus M and N proteins by partial chemical cleavage

Distinct binding sites for zinc and double-stranded RNA in the reovirus outer capsid protein sigma 3

By atomic absorption analysis, we determined that the reovirus outer capsid protein sigma 3, which binds double-stranded RNA (dsRNA), is a zinc metalloprotein. Using Northwestern blots and a novel zinc blotting technique, we localized the zinc- and dsRNA-binding activities of sigma 3 to distinct V8 protease-generated fragments. Zinc-binding activity was contained within an amino-terminal fragment that contained a transcription factor IIIA-like zinc-binding sequence, and dsRNA-binding activity was associated with a carboxy-terminal fragment. By these techniques, new zinc- and dsRNA-binding activities were also detected in reovirus core proteins. A sequence similarity was observed between the catalytic site of the picornavirus proteases and the transcription factor IIIA-like zinc-binding site within sigma 3. We suggest that the zinc- and dsRNA-binding activities of sigma 3 may be important for its proposed regulatory effects on viral and host cell transcription and translation.

Distinct binding sites for zinc and double-stranded RNA in the reovirus outer capsid protein sigma 3

By atomic absorption analysis, we determined that the reovirus outer capsid protein sigma 3, which binds double-stranded RNA (dsRNA), is a zinc metalloprotein. Using Northwestern blots and a novel zinc blotting technique, we localized the zinc- and dsRNA-binding activities of sigma 3 to distinct V8 protease-generated fragments. Zinc-binding activity was contained within an amino-terminal fragment that contained a transcription factor IIIA-like zinc-binding sequence, and dsRNA-binding activity was associated with a carboxy-terminal fragment. By these techniques, new zinc- and dsRNA-binding activities were also detected in reovirus core proteins. A sequence similarity was observed between the catalytic site of the picornavirus proteases and the transcription factor IIIA-like zinc-binding site within sigma 3. We suggest that the zinc- and dsRNA-binding activities of sigma 3 may be important for its proposed regulatory effects on viral and host cell transcription and translation.

Mapping regions of the matrix protein of vesicular stomatitis virus which bind to ribonucleocapsids, liposomes, and monoclonal antibodies

The matrix (M) protein of vesicular stomatitis virus (VSV) appears to function as a bridge between the ribonucleocapsid (RNP) core and the envelope in assembly of the virion. Two such properties would necessitate at least one site for interaction with the nucleocapsid and one with the envelope. In this study M protein was found to mediate the in vitro binding to RNP cores of phospholipid vesicles, representing membrane structures. The M protein could bind initially to either the vesicles or the RNP cores to promote RNP-vesicle association. A trypsin-resistant fragment (MT) of M protein, missing the initial 43 amino acids from its amino terminus, reconstituted with acidic phospholipid vesicles with the same binding efficiency as did whole M protein, suggesting that the carboxy-terminal 81% retained those regions of the M protein which interact with a lipid bilayer. The MT protein, however, was considerably less efficient than intact M protein as an inhibitor of in vitro virus transcription; almost 2.5-fold more MT protein than intact M protein was required for 50% inhibition of VSV transcription, indicating that a site for interaction with the RNP core may have been lost. A monoclonal antibody which is able to reverse the in vitro inhibition of transcription by M protein did not react by immunoblotting with MT protein. Partial tryptic digests of the M protein probed with this monoclonal antibody indicated that epitope 1 lies between amino acid residues 18 and 43. This region appears to be a site that promotes interaction of the M protein with the RNP core of VSV. Monoclonal antibodies to epitopes 2 and 3, which exhibit some overlap in binding to M protein but do not reverse transcription inhibition, were mapped by cleavage with N-chlorosuccinimide at regions in a carboxy direction from epitope 1.

Phosphorylation sites on phosphoprotein NS of vesicular stomatitis virus

The phosphoprotein NS of vesicular stomatitis virus which accumulates within the infected cell cytoplasm is phosphorylated at multiple serine and threonine residues (G. M. Clinton and A. S. Huang, Virology 108:510-514, 1981; Hsu et al., J. Virol. 43:104-112, 1982). Using incomplete chemical cleavage at tryptophan residues, we mapped the major phosphorylation sites to the amino-terminal half of the protein. Analysis of phosphate-labeled tryptic peptides suggests that essentially all of the label is within the large trypsin-resistant fragment predicted from the sequence of Gallione et al. (J. Virol. 39:52-529, 1981). A similar result has been obtained for NS protein isolated from the virus particle by C.-H. Hsu and D. W. Kingsbury (J. Biol. Chem., in press). Analysis of phosphodipeptides utilizing the procedures of C. E. Jones and M. O. J. Olson (Int. J. Pept. Protein Res. 16:135-142, 1980) enabled us to detect as many as six distinct phosphate-containing dipeptides. From these studies, together with the known sequence data, we conclude that the major phosphate residues on cytoplasmic NS protein are located in the amino third of the NS molecule and most probably between residues 35 and 106, inclusive. The studies also provide formal chemical proof that NS protein has a structure consistent with a monomer of the sequence of Gallione et al. as modified by J. K. Rose (personal communication). The low electrophoretic mobility of this protein on sodium dodecyl sulfate-polyacrylamide gel electrophoresis is not therefore due to dimerization.