title: Mung bean nuclease cleavage of a dA + dT-rich sequence or an inverted repeat sequence in supercoiled PM2 DNA depends on ionic environment.
abstract: We have determined the nucleotide sequences around two alternative sites cleaved in supercoiled PM2 DNA by single-strand-specific mung bean nuclease in different ionic environments. In 10 mM Tris-HC1 (pH 7.0, 37 degrees C), the major site is a dA+dT-rich sequence which maps with a known early denaturation region at 0.75 map units. About 30 cleavages occurred in a 135 bp region. Cleavages were largely excluded at (dA)n . (dT)n (n = 3-7) sequences. Cleavage patterns of this type have not been previously observed in dA+dT-rich sequences. With the addition of 0.1 M NaC1 the major alternative site occurred in a hyphenated inverted repeat sequence 500 bp away (0.70 map units) and did not map to an early denaturation region. One major and 4 minor cleavages occurred in the region between the repeats, suggesting that a hairpin containing at most a 12 bp stem and 10 base loop is recognized. The basis for nuclease recognition of the dA+dT-rich sequence is not clear. The differences in the sequences and cleavage patterns at the alternative sites indicate that their secondary structures differ.
mesh_terms: D001435:Bacteriophages; D001483:Base Sequence; D004262:DNA Restriction Enzymes / Q000378:metabolism; D004277:DNA, Single-Stranded; D004278:DNA, Superhelical; D004279:DNA, Viral; D004720:Endonucleases / Q000378:metabolism*; D011549:Pseudomonas; D012091:Repetitive Sequences, Nucleic Acid; D015719:Single-Strand Specific DNA and RNA Endonucleases; D013379:Substrate Specificity
chemical_list: D004277:DNA, Single-Stranded; D004278:DNA, Superhelical; D004279:DNA, Viral; D004720:Endonucleases; D004262:DNA Restriction Enzymes; D015719:Single-Strand Specific DNA and RNA Endonucleases