The molecular karyotype of the megabase chromosomes of Trypanosoma brucei stock 427

We present the molecular karyotype of the megabase chromosomes of Trypanoso ma brucei stock 427, clone 221a. This cloned stock is most commonly used in research laboratories in genetic manipulation experiments and in studies o f antigenic variation. Using 116 previously characterised chromosome-specif ic markers, we identify 11 diploid pairs of megabase chromosomes and detect no loss of synteny in EST and gene marker distribution between this stock and the genome project reference stock TREU 927/4. Nevertheless, the chromo somes of 427 are all larger than their homologues in 927, except chromosome s IIa and IXa. The greatest size variation is seen in chromosome I, the sma llest of which is 1.1 Mb (927-Ia) and the largest 3.6 Mb (427-Ib). The tota l nuclear DNA. content of both stocks has been estimated by comparison of t he mobility of T. brucei and yeast chromosomes. Trypanosomes of stock 427 c ontain approximately 16.5 Mb more megabase chromosomal DNA than those of st ock 927. We have detected the presence of bloodstream-form expression-site- associated sequences on eight or more megabase chromosomes. These sequences are not found on the same chromosomes in each stock. We have determined th e chromosomal band location of nine characterised variant surface glycoprot ein genes, including the currently expressed VSG 221. Our results demonstra te both the stability of the T. brucei genome, as illustrated by the conser vation of syntenic groups of genes in the two stocks, and the polymorphic n ature of the genomic regions involved in antigenic variation. We propose th at the chromosomes of stock 427 be numbered to correspond to their homologu es in the genome project reference stock TREU 927/4. (C) 2000 Elsevier Scie nce B.V. All rights reserved.