A single amino acid change restores DNA cytosine methyltransferase activity in a cloned chlorella virus pseudogene.
The chlorella virus PBCV-1 contains an open reading frame, named P17-ORF4, which differs by eight amino acids from a DNA cytosine methyltransferase, M.CviJI, encoded by a different chlorella virus IL-3A. Whereas IL-3A expresses M.CviJI, which methylates the central cytosine in (A/G)GC(T/C/G) sequences, P17-ORF4 is non-functional. Gene fusions between P17-ORF4 and M.CviJI and site-directed point mutations revealed that changing Gln188 to Lys188 abolishes M.CviJI methyltransferase activity. Conversely, changing Lys188 in P17-ORF4 to Gln188 results in M.CviJI activity. The other altered seven amino acids do not appear to affect M.CviJI activity.
Zhang
Y
Y
Department of Plant Pathology, University of Nebraska, Lincoln 68583-0722.
Nelson
M
M
Van Etten
J L
JL
D000595:Amino Acid Sequence; D001483:Base Sequence; D002708:Chlorella; D003001:Cloning, Molecular; D015257:DNA-Cytosine Methylases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011544:Pseudogenes / Q000235:genetics*; D015183:Restriction Mapping; D014780:Viruses / Q000201:enzymology* / Q000235:genetics
D015257:DNA-Cytosine Methylases