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Abstract Conditions have been established under which Micrococcus luteus ultraviolet exonuclease cleaves off part of the 12-nucleotide-long single-stranded cohesive ends of λDNA, leaving either 3 or 4 nucleotides on each end, as determined by the repair incorporation of radioactive nucleotides into the remaining single-stranded ends by DNA polymerase I. This finding is supported by results from nearest neighbor and 3' end analyses which indicate that the cleavage is almost, but not completely, synchronous. The ultraviolet exonuclease-digested λDNA can be further degraded by Escherichia coli exonuclease III to increase the length of the single-stranded ends. After repair synthesis, the nucleotide sequence of the newly exposed segments can be determined without having to repeat the sequence analysis of the entire cohesive ends. The λDNA digested this way gave the expected incorporation of nucleotides by DNA polymerase I.
Ghangas et al. (Sun,) studied this question.