Structure Of Capsid Protein Research Articles

Evidence that a phage T4 DNA packaging enzyme is a processed form of the major capsid gene product

A phage T4 DNA packaging enzyme appears to arise as a processed form of the major T4 capsid structural protein gp23. The enzyme activity and antigen are missing from all head gene mutants that block the morphogenetic proteolytic processing reactions of the head proteins in vivo. The enzyme antigen can be formed in vitro by T4 (gp21) specific processing of gp23 containing extracts. Enzyme antigen is found in active processed proheads but not in full heads. The enzyme and the major capsid protein show immunological cross-reactivity, produce common peptides upon proteolysis, and share an assembly-conformation-dependent ATP binding site. The packaging enzyme and the mature capsid protein (gp23∗) both appear to arise from processing of gp23, the former as a minor product of a specific gp23 structure in the pro-head, acting in DNA packaging as a DNA-dependent ATPase, and a headful-dependent terminase.

Nucleotide sequence of the coat protein gene of canine parvovirus.

The nucleotide sequence of the canine parvovirus (CPV2) from map units 33 to 95 has been determined. This includes the entire coat protein gene and noncoding sequences at the 3' end of the gene, exclusive of the terminal inverted repeat. The predicted capsid protein structures are discussed and compared with those of the rodent parvoviruses H-1 and MVM.

Regulation of viral transcription and DNA replication by the SV40 large T antigen.

Simian Virus 40 (SV40) provides a particularly useful model for studying gene regulation at the molecular level because it is one of the simplest and most thoroughly characterized (Tooze 1980) viral systems known to undergo a well-defined developmental cycle in mammalian cells. The entire nucleotide sequence of the 5243 base pair genome of SV40 has been determined (Reddy et al. 1978; Fiers et al. 1978) and important regions such as the origin of replication, transcriptional promoters, structural gene boundaries, splice junctions, and positions of mutations have been located. The small double-stranded circular genome of SV40 encodes only five or six genes and consequently relies in large part on the host cell machinery to carry out complex regulated processes such as transcription and replication. During lytic infection of monkey cells, SV40 undergoes a temporal pro-gram of gene expression that is controlled in part by viral coded proteins (Tegtmeyer1972; Cowan et al. 1973; Tegtmeyer et al. 1975; Reed et al. 1976). Immediately after infection, the SV40 A and F genes, encoding the large T (Black et al. 1963; Tegtmeyer1975) and small t (Prives et al. 1978; Crawford et al. 1978; Sleigh et al. 1978) antigens respectively, are expressed. Transcription of these early viral genes by the host RNA polymerase II originates from a region of the genome located at approximately 0.67–0.70 fractional units on the conventional genome map (Fig. 1) (Sambrook et al. 1973; Khoury et al. 1973; Jackson and Sugden 1972; Khoury et al. 1975). During this early phase of the lytic cycle, SV40 DNA replication does not occur (Tegtmeyer 1912) and expression of the structural capsid proteins is detectable only at very low levels (Cowan et al. 1973; Alwine et al. 1977).

Semliki Forest virus-specific nonstructural protein is associated with ribosomes

Received 25 September 1979 1. Introduction Semliki Forest virus (SFV) 42 S RNA genome codes probably for eight different polypeptides. Four of these are nonstructural proteins with mol. wt 70 000 (ns70), 86 000 (ns86), 72 000 (ns72) and 60 000 (ns60). They are translated as a giant polyprotein in the above order [ 1,2]. At least three of them have been found in association with the RNA replication com- plex [3]. The structural proteins, capsid protein and envelope glycoproteins El, E2 and E3, are translated from a subgenomic 26 S mRNA as a 130 000 mol. wt polyprotein [4,5]. The amino-terminal capsid protein is cleaved from the growing polyprotein before the translation of the envelope proteins starts [S ,6]. The nascent envelope proteins penetrate the ER membrane, become glycosylated and are transported to the plasma membrane [ 5,6]. After cleavage the capsid protein remains associated with the polysomal ribosomes until it is transferred to the nucleocapsid (which consists of 42 S RNA and capsid proteins, [4,5]) or is released to the monosome pool after the translation of the polyprotein has been completed [7-91. Here we report that one of the nonstructural pro- teins, ns86, is also associated with ribosomes and can be crosslinked with the ribosomal RNAs by ultraviolet irradiation. 2. Materials and methods The origin and cultivation of the SFV prototype strain in HeLa and BHK21 cells have been described [3,8]. For labeling of ribosomal RNAs the cells were

Properties and amino acid composition of polyoma virus purified by zonal ultracentrifugation

Virion and capsid preparations of three different strains of polyoma virus have been purified by the use of the Anderson zonal ultracentrifuge. This technique permits good recovery of the infectivity of large volumes of virus-infected mouse kidney cell lysates and yields polyoma virion and capsid preparations with a high degree of purity, as determined by equilibrium density-gradient centrifugation, band- and boundary-centrifugations, and by chemical composition analysis. Briefly, the procedure consists of the concentration of the virus particles by ammonium sulfate precipitation (50% saturation), extraction of the particles from the precipitate with 0.5% sodium deoxycholate, 0.02 m Tris-HCl (pH 9.0) and the fractionation of the virions and capsids by centrifugation in the zonal ultracentrifuge. The amino acid compositions of purified virion and capsid preparations representing three strains of virus have been determined. The virion preparations have a higher content of lysine, arginine and alanine and a lower content of aspartate, methionine and leucine, when compared to capsids of the same strain. It is suggested that the virions contain a basic polypeptide in addition to the structural capsid protein present in both virions and capsids. The amino acid compositions of the two large-plaque strains have been found to be similar. The small-plaque strain contains more lysine and serine residues and less methionine, when compared to either of the large-plaque strains. The immunologic reactivities of the three strains, determined by complement fixation, are in agreement with the amino acid analyses. The two large-plaque strains are antigenically identical; the small-plaque particles are significantly different from the large-plaque particles.