A geminivirus replication protein is a sequence-specific DNA binding protein.

Abstract

The genome of the geminivirus tomato golden mosaic virus (TGMV) consists of two circular DNA molecules designated as components A and B. The A component encodes the only viral protein, AL1, that is required for viral replication. We showed that AL1 interacts specifically with TGMV A and B DNA by using an immunoprecipitation assay for AL1:DNA complex formation. In this assay, a monoclonal antibody against AL1 precipitated AL1:TGMV DNA complexes, whereas an unrelated antibody failed to precipitate the complexes. Competition assays with homologous and heterologous DNAs established the specificity of AL1:DNA binding. AL1 produced by transgenic tobacco plants and by baculovirus-infected insect cells exhibited similar DNA binding activity. The AL1 binding site maps to 52 bp on the left side of the common region, a 235-bp region that is highly conserved between the two TGMV genome components. The AL1:DNA binding site does not include the putative hairpin structure that is conserved in the common regions or the equivalent 5' intergenic regions of all geminiviruses. These studies demonstrate that a geminivirus replication protein is a sequence-specific DNA binding protein, and the studies have important implications for the role of this protein in virus replication.

Evidence that DNA-A of a geminivirus associated with severe cassava mosaic disease in Uganda has arisen by interspecific recombination.

“…In addition, the sequence ATTGGCTG at nt 1-8 in isolate C39 is followed by AATCGGTG at nt 44-51, AATGGGGG at nt 53-60 and the nearly complementary sequence TAACCCCC at nt 84-77. In other geminiviruses, nearly reiterated sequences of this kind interact with the AC1 gene product during viral DNA replication (Fontes et al, 1992 ;Argu$ ello-Astorga et al, 1994).…”

Replication promiscuity of DNA-β satellites associated with monopartite begomoviruses; deletion mutagenesis of the Ageratum yellow vein virus DNA-β satellite localizes sequences involved in replication

“…Replication of DNA-A and DNA-B components relies on an interaction between the DNA-A-encoded replicationassociated protein (Rep) and reiterated motifs (termed iterons) located within the origin of replication (Argüello-Astorga et al, 1994;Fontes et al, 1992Fontes et al, , 1994Laufs et al, 1995;Gladfelter et al, 1997), which usually limits Rep trans-replication to its own DNA-A and DNA-B components. In contrast, the ability of intact and defective DNA-b satellites to be trans-replicated by distinct begomoviruses (Dry et al, 1997;Saunders et al, 2002;Mansoor et al, 2003) indicates that productive origin recognition is more relaxed for the satellite.…”

Lethal Mutations Within the Conserved Stem-loop of African Cassava Mosaic Virus DNA are Rapidly Corrected by Genomic Recombination

“…The product of gene AC1 is the only virus-encoded protein essential for ACMV DNA replication (Etessami et al, 1991). The protein from the related virus tomato golden mosaic virus (TGMV) binds in vitro to TGMV sequences located upstream of the stem-loop, but not to the stem-loop itself (Fontes et al, 1992). However, the analysis of TGMV and squash leaf curl virus (SqLCV) recombinants containing chimeric common region sequences has demonstrated that the stem loop structure is also an integral part of the replication origin (Lazarowitz et al, 1992).…”