A collection of yeast strains bearing single marked Ty1 insertions on chromosome III was generated. Over 100 such insertions were physically mapped by pulsed-field gel electrophoresis. These insertions are very nonrandomly distributed. Thirty-two such insertions were cloned by the inverted PCR technique, and the flanking DNA sequences were determined. The sequenced insertions all fell within a few very limited regions of chromosome III. Most of these regions contained tRNA coding regions and/or LTRs of preexisting transposable elements. Open reading frames were disrupted at a far lower frequency than expected for random transposition. The results suggest that the Ty1 integration machinery can detect regions of the genome that may represent "safe havens" for insertion. These regions of the genome do not contain any special DNA sequences, nor do they behave as particularly good targets for Ty1 integration in vitro, suggesting that the targeted regions have special properties allowing specific recognition in vivo.
Bibliographical noteFunding Information:
We gratefully acknowledge P. Hieter. C. Connelly, and S. Tugen-dreich for helpful discussions on pulsed-field gel electrophoresis and computer analyses. We thank the individuals acknowledged in the text for plasmids and S. Oliver for providing statistics on the chr Ill DNA sequence. H. J. was supported by a Howard Hughes Medical Fellowship and a Lamport Research Award, M. A. 8. was supported by National Institutes of Health (NIH) predoctoral training grant T32 GM07445, L. T. B. was supported by National Science Foundation predoctoral training grant RCD-9154644, D. F. V. was a Genentech Fellow of the Life Sciences Foundation, and G. N. was supported by Damon RunyonMlalter Winchell Cancer Fund Fellowship DRG-044. Supported in part by grant GM36481 from the NIH and an American Cancer Society Faculty Research Award to J. D. B.