An aberrant cleavage in the mengovirus polyprotein and its role in the expression of the interferon-sensitive mutant is-1
Abstract
Interferon can inhibit the growth of all viruses, yet is not effective therapeutically. This thesis investigates the difference between a wild type mengovirus and its interferon-sensitive mutant (is-1). Mengovirus RNA, like all picornaviruses, is translated into a polyprotein which is proteolytically processed in several steps. The precursor (L-1ABCD-2A) to the capsid proteins is liberated while the polyprotein is being translated. From it, the leader peptide (L) is removed concomitant with the addition of myristic acid (CH$\sb3$(CH)$\sb{12}$COOH) to the amino-terminus. Myristylation is required for proteolysis of 1ABCD-2A, the formation of mature virions, and the release of RNA from the virion in subsequent infections. In infected cells, is-1 produced an unstable, 10.6 kd peptide with an amino-terminal sequence consistent with L. The 10.6 kd peptide appeared to be derived from an aberrant cleavage of L since a slightly larger, analogous peptide was found in is$\sp{+}$ infected cells. Such an aberrant cleavage would delay myristylation of 1ABCD-2A, with lethal consequences for is-1 in interferon-treated cells. is-1 appeared structurally identical to the wild type, yet the is-1 virions were more sensitive to pH 2. Of 8 pH 2 stable isolates of is-1, two were resistant to interferon. Nevertheless, like is-1, all 8 produced an unstable 10.6 kd polypeptide. Only two of the pathways by which interferon inhibits virus growth are well defined: the 2-5(A)$\sb{\rm n}$ synthetase and protein kinase pathways. Both are expressed in two subclones of mouse L cells, G3 and TA6. These pathways do not mediate IFN's effects against is-1 because this virus is only inhibited in G3 cells. Two additional cardioviruses, m-mengovirus and encephalomyocarditis-R (EMC-R), were grown on G3 and TA6 cells. m-Mengovirus growth, like is$\sp{+}$, was delayed in interferon-treated G3 and TA6 cells. EMC-R, like is-1, was sensitive to interferon in G3, but not TA6 cells. However, is-1 and EMC-R were not identical. Only is-1 was rescued by actinomycin D, induced interferon, and expressed a 10.6 kd protein. Thus, the anti-cardiovirus activities which inhibit is-1 and EMC-R are distinct from the 2-5(A)$\sb{\rm n}$ synthetase and protein kinase pathways and from each other.
Degree
Ph.D.
Advisors
Simon, Purdue University.
Subject Area
Microbiology
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.
