Branch migration of a DNA Holliday junction is a key step in genetic recombination. Previously, it was shown that a single base-pair heterology between two otherwise identical DNA sequences is a substantial barrier to passage of a Holliday junction during spontaneous branch migration. Here, we exploit this inhibitory effect of sequence heterology to estimate the step size of branch migration. W...

We have examined the effects of placing nonhomologous DNA on the ends of an insertion-type gene targeting vector. The presence of terminal heterologies was found to be compatible with insertion targeting, and the terminal heterologies were efficiently removed. Terminal heterologies reduced the frequency of gene targeting to variable extents. The degree of inhibition of targeting was dependent o...

Mammalian cells are able to repair chromosomal double-strand breaks (DSBs) both by homologous recombination and by mechanisms that require little or no homology. Although spontaneous homologous recombination is rare, DSBs will stimulate recombination by 2 to 3 orders of magnitude when homology is provided either from exogenous DNA in gene-targeting experiments or from a repeated chromosomal seq...

RecA protein promotes an unexpectedly efficient DNA strand exchange between circular single-stranded DNA and duplex DNAs containing short (50-400-base pair) heterologous sequences at the 5' (initiating) end. The major mechanism by which this topological barrier is bypassed involves DNA strand breakage. Breakage is both strand and position specific, occurring almost exclusively in the displaced ...

The synthetic method for haptens of organophosphorus (OP) pesticides with a spacer arm (amino carboxylic acid) attached at the pesticide thiophosphate group was simplified to a large extent. While the previous synthetic approach for this type of haptens requires seven steps, the present process involves only two steps. Using this process, five haptens of fenthion differing in spacer arm length ...

During recombination-mediated repair of DNA double-strand breaks, strand transfer proteins must distinguish a homologous repair template from closely related genomic sequences. However, some tolerance by strand transfer proteins for sequence differences is also critical: too much stringency will prevent recombination between different alleles of the same gene, but too much tolerance will lead t...

An enzyme-linked immunosorbent assay for neopterin using penicillinase as marker enzyme is reported here by polyclonal antibodies against neopterin conjugated to bovine serum albumin which were raised in rabbits. Immunoglobulin fractions were purified and coated on wells of microtiter plates. A chain heterology was introduced in neopterin derivative and conjugated to penicillinase. The assa...