Distribution of the ardA family of antirestriction genes on conjugative plasmids

Abstract

The ardA gene of I1 plasmid Collb-P9 was previously shown to alleviate DNA restriction by type I enzymes and to promote conjugative transmission of the unmodified plasmid to a restricting host. To clarify the ecological role of s d A , its distribution was determined on plasmids from 23 incompatibility groups using hybridization to the coding sequence as an assay. Hybridizing sequences, shown by nucleotide sequencing to have at least 60% identity with a d A , were detected on plasmids belonging to the I complex (IncB, I1 and K), the F complex (IncFV) and the lncN group. The a d A homologues were found to specify an antirestriction phenotype which was enhanced by genetic derepression of the plasmid transfer system. a d A loci map in plasmid leading regions but show no consistent association with a particular type of origin-oftransfer or a leading region gene of the ssb (single-stranded DNA-binding protein), psis (plasmid SOS inhibition) and hok (host killing) families. It may be significant that a d A + plasmids are authentic enterobacterial plasmids and that type I restriction systems are associated historically with members of the Enterobacteriaceae.

Importance of integrons in the diffusion of resistance

“…Examples of these defensive-mechanisms include reducing the number of restriction target sites or encoding antirestriction systems (e.g. methylation systems) [5,9,14,97].…”

DNA Mimicry by Antirestriction and Pentapeptide Repeat (PPR) Proteins

“…ArdA and Ocr differ considerably in their ability to inhibit the methylase (modification) activity of EcoKI-like enzymes. As a rule, if ardA and 0.3(ocr) genes are governed by a strong promoter, antirestriction and antimodification activities of ArdA and Ocr are established simultaneously ( Delver et al, 1991;Chilley & Wilkins, 1995;Atanasiu et al, 2002). Some data suggest, however, that the inhibition of endonuclease and methylase activities depends on different interactions of ArdA proteins with type I RM enzymes.…”

“…ardA genes were first discovered in plasmids of the incompatibility group N in 1984-1985(Belogurov et al,1985, and later in other types of plasmids (Kotova et al, 1988;Delver et al, 1991). In 1991-1995, ardA genes were sequenced and the primary structure of ArdA proteins was determined (Delver et al, 1991;Chilley & Wilkins, 1995). Genes ardA are located in the leader region of the plasmid sequence, which lies next to oriT and is the first to enter the host cell in the course of conjugative transfer.…”

How Does the Horizontal Gene Transfer in Bacteria Occur and Than Is It Tied Up

“…Мута-ционное появление в геноме нового сайта рестрикции может снизить возможность успешного исхода ОГПГ. Коньюгативные плазмиды, содержащие системы анти-рестрикции (в частности, ген ardA) более стабильны в клетках хозяев с активными рестриктазами I типа [17]. Вместе с тем, расщепление донорной ДНК рестрик-тазами на мелкие фрагменты оказывает рекомбино-генный эффект и может приводить к возникновению внутригенной мозаики.…”