Worm Breeder's Gazette 13(1): 90 (October 1, 1993)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Recombination suppression by integrated high-copy arrays

Jeff Way, Alice Ye Wang.

Dept. of Biology, Nelson Labs, Rutgers University, Piscataway NJ 08855.

On two occasions we have run into problems trying to recombine linked markers with integrated high copy arrays of injected plasmids.

jeIn2 is an integration of a mec-3 -lacZfusionplasmid plus a 'Twitcher' marker plasmid into the right arm of chromosome IV. It has been possible to recombine this element with mec-3 and dpy-20 ,and these markers appear to be less than 5 map units to the right of the integrated array. However, we have not been able to generate true recombinants containing jeIn2 and the distal markers ced-3 , ham-1 ,or dpy-4 .From a jeIn2 + / + dpy-4 heterozygote, occasional Dpy Twi animals can be isolated. Instead of finding that 1/3 of their Dpy Twi offspring are homozygous for the jeIn2 element, we find that all of the Twi animals have non-Twi progeny. To explain this, we invoke two ideas: 1) the integrated array suppresses recombination distal to itself, and 2) the integrated array can, at some frequency, excise and generate an unstable extrachromosomal array. The fate of the chromosome from which the array excises is unclear, as it is selected against when isolating these ''recombinants."

We have observed apparent excision in crosses with jeIn2 and ham-1 and with jeIn1 ( mec-7 -lacZon Chr. I) and lin-17 .Both these arrays can undergo normal recombination with centrally located markers. Both arrays were generated by gamma ray-mediated integration of an extrachromosomal array. We have not examined oligonucleotide-generated arrays for recombination suppression.

It is worth remembering that an integrated array that contains 100 copies of a 10kb plasmid would be 1 Mb in length, and it seems plausible that such an insertion could disrupt chromosome pairing. Also, since the arrays contain many repeated copies of one or two plasmids, they could undergo internal homologous recombination to generate an extrachromosomal circle. It might be possible to use large integrated arrays to look for sites that mediate chromosome pairing for recombination.