CHARACTERISTICS OF THE LARGE (DA)(DT) HOMOPOLYMER TRACTS IN D-DISCOIDEUM GENE FLANKING AND INTRON SEQUENCES

D. discoideum, the slime mold, is one of the most AT rich eukaryotic g enomes known. In this paper we examine this organism's database for ov erlapping N-tuples of high frequency and find A and T tracts possess a mong the highest frequencies in flanking sequences but not in coding s equences. We examined both overlapping and non-overlapping frequencies of the A, T, G and C homopolymer tracts of 2 < N < 6. Overlapping (dG ).(dC) and (dA).(dT) tracts occur at greater frequencies than expected , based on random occurrence. Long (dA).(dT) tracts of N > 10 occur at well above expected frequencies in flanking and intron regions, while (dG).(dC) tracts above N = 5 are rarely found. Some of the implicatio ns of these findings for tract origins in slip-strand replication and for chromatin stucture are discussed.