Analysis of double-strand-break repair by Chlorella retrotransposon Zepp.

To elucidate the contribution of LINE-like retrotransposon Zepps in formation and maintenance of chromosomal telomeres, newly formed mini-chromosomes in irradiated Chlorella vulgaris cells were isolated and structurally characterized. A mini-chromosome Y32 (approximately 400 kbp in size) was shown to have several copies of Zepp elements on both termini. On the right arm terminus, two copies of Zepps were found in a tandem array with poly(A) tracts facing towards the chromosome end. The poly(A) tail and a 3'-end of approximately 400 bp of the distal copy was replaced by telomeric repeats. On 5'-side of the proximal copy was another Zepp element in a reversed orientation. This newly formed telomeric structure is very similar to that found in the left arm terminus of chromosome I and support the model of Zepp-mediated maintenance of Chlorella telomeres.