We present the molecular karyotype of
the megabase chromosomes of Trypanosoma brucei stock 427, clone 221a.
This cloned stock is most commonly used in research laboratories in
genetic manipulation experiments and in studies of antigenic
variation. Using 116 previously characterised chromosome-specific
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 chromosomes of 427 are all larger than their
homologues in 927, except chromosomes IIa and IXa. The greatest size
variation is seen in chromosome I, the smallest of which is 1.1 Mb
(927-Ia) and the largest 3.6 Mb (427-Ib). The total nuclear DNA
content of both stocks has been estimated by comparison of the
mobility of T. brucei and yeast chromosomes. Trypanosomes of stock
427 contain approximately 16.5 Mb more megabase chromosomal DNA than
those of stock 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 the chromosomal band location of nine
characterised variant surface glycoprotein genes, including the
currently expressed VSG 221. Our results demonstrate both the
stability of the T. brucei genome, as illustrated by the conservation
of syntenic groups of genes in the two stocks, and the polymorphic
nature of the genomic regions involved in antigenic variation. We
propose that the chromosomes of stock 427 be numbered to correspond
to their homologues in the genome project reference stock TREU 927/4.
(C) 2000 Elsevier Science B.V. All rights reserved.