Structural organization and polypeptide composition of the avian adenovirus core

Abstract

CELO virus (fowl adenovirus 1) contained three core polypeptides of molecular weights 20,000, 12,000, and 9,500. The core was similar to that of human adenoviruses, with some evidence of compact subcore domains. Micrococcal nuclease digestion of CELO virus cores produced a smear of DNA fragments of gradually decreasing size, with no nucleosome subunit or repeat pattern. Moreover, when digested cores were analyzed without protease treatment, there was again no evidence of a nucleosome substructure; neither DNA fragments nor core proteins entered a 4% polyacrylamide gel. The organization of the core is thus quite unlike that of chromatin. Restriction endonuclease analysis of the DNA from digested cores showed that the right end was on the outside of the core. We suggest that adenovirus DNA is condensed into the core by cross-linking and neutralization by the core proteins, beginning with the packaging sequence at the center of the core and ending with the right end of the DNA on the outside. Adenoviruses contain an internal core that consists of the viral DNA and the virus-coded, basic core proteins. In human adenovirus, there are two prominent arginine-rich core proteins, the major core protein (polypeptide VII) and the minor core protein (polypeptide V). Of the two, the major core protein is more tightly associated with the viral DNA (4, 14, 15). A third virion polypeptide, designated [i, which is very small and very rich in arginine, may also be associated with the viral DNA (25). The adenovirus terminal protein (43, 44) is covalently linked to the 5' ends of the viral genome. The structure of the adenovirus core has been investigated by electron microscopy, and several different morphological structures have been proposed. Brown et al. (4) proposed that the core was organized into 12 morphological subunits, each under a vertex of the capsid. However, Nermut (38, 39) suggested that the viral DNA was wrapped around a helical filament composed of the major core protein, and that the resulting nucleoprotein was packed into six rodlike elements.

Isolation and characterization of adenovirus core nucleoprotein subunits

“…Viral nucleoprotein species migrating more slowly than cellular mononucleosomes were previously observed when intracellular Ad2 DNA was digested with micrococcal nuclease (29) but were not detected after micrococcal nuclease digestion of CELO virus cores (15). Differences in the experimental conditions, for example, the purification of cores before nuclease digestion, might account for the differences between the results reported here and those of Li et al (15).…”

“…Viral nucleoprotein species migrating more slowly than cellular mononucleosomes were previously observed when intracellular Ad2 DNA was digested with micrococcal nuclease (29) but were not detected after micrococcal nuclease digestion of CELO virus cores (15). Differences in the experimental conditions, for example, the purification of cores before nuclease digestion, might account for the differences between the results reported here and those of Li et al (15). In this context, we cannot emphasize too strongly that cores released from human adenovirions are fragile, unstable structures whose morphology and biochemical properties are strongly influenced by their in vitro environment (20,31).…”

VA RNAs from avian and human adenoviruses: dramatic differences in length, sequence, and gene location

“…However, with the orientation shown in Fig. 2, the positions of the genes coding for the T antigens (30), as well as the DNA sequence required for encapsidation, are oriented toward the left end of the genome (20) as is the case with the human adenoviruses. With the opposite orientation, the CELO VA RNA gene would be placed on the left side, transcribed in the rightward direction but still displaced about 20 map units relative to the genes for the human VA RNAs.…”

Characterization of CELO Virus Proteins That Modulate the pRb/E2F Pathway

“…Both adenovirus types form icosahedral capsids of 70 to 75 nm, with hexons and pentons as the major subunits (12,13,24,32,35,38,43,47). The viral capsids contain a linear double-stranded DNA molecule that is associated with viral core proteins (34). Replication and viral assembly occur in the nucleus of the infected cell (8,36,46).…”