The chromosome ends of Saccharomyces cerevisiae are complex mosaics of several different types of telomeric and subtelomeric elements known as X element core sequences, X element combinatorial repeats, telomeric repeats, and Y' elements (2). The X element core sequence, a small conserved element of ~475 bp containing an ARS sequence and in most cases an Abf1p binding site, is the only region shared by all chromosome ends (2, 1). The X element combinatorial repeats, formerly known as subtelomeric repeats or STRs, are located between the X element core sequence and the telomeric end and are usually present as a combination of one or more of several types of smaller elements designated D, C, B, or A (2, 1). The telomeric repeat is a G-rich terminal sequence of the form (TG_1-3)_n that is maintained by telomerase (1). The Y' element is a helicase-encoding repetitive sequence found in many but not all subtelomeric regions next to the telomeric repeats, or adjacent X element combinatorial repeats, either as a single copy or tandem repeat of two to four copies (3, 1, 4). Possible functions of telomeric regions include roles in chromosomal segregation, maintenance of chromosome stability, recombinational sequestering, or as a barrier to transcriptional silencing (2, 1).

TEL04R, the right telomeric region of chromosome IV, is composed of an X element core sequence TEL04R-XC containing an ARS consensus sequence, an Abf1p binding site and a dubious ORF YDR543C, X element combinatorial repeats TEL04R-XR of the D, C, B and A types containing Tbf1p binding sites and spanning dubious ORF YDR544C, a short stretch of telomeric repeats TEL04R-TR also spanning dubious ORF YDR544C, and a long Y' (Y'-L) element TEL04R-YP containing an ARS consensus sequence, a region of 36-bp repeats, a verified ORF YRF1-1/YDR545W and a dubious ORF YDR545C-A.

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Further information can be found at the website of Dr. Ed Louis, Institute of Genetics, The University of Nottingham.

Last updated: 2003-10-29