Chromosomal environment of a trypanosome metacyclic VSG gene expression site

The gene encoding the metacyclic Variant Surface Glycoprotein (VSG) ILTat 1.22 is expressed in situ from a monocistronic, telomeric transcription unit in metacyclic-derived trypanosomes. The genomic environment upstream of the 1.22 basic copy gene (1.22BC) is composed of single copy, transcriptionally silent sequence. This sequence occurs in an area which, in bloodstream VSG gene expression sites, is thought to be subject to the influence of a developmentally regulated position silencing effect. For this reason, the silent area upstream of the 1.22BC is designated as a 'metacyclic domain'. The metacyclic domain is defined as any single copy, silent sequence linked with the M-VSG gene. In a step towards understanding the nature of the control of M-VSG gene expression, efforts to define the extent of the metacyciic domain for the ILTat 1.22 M-VSG gene were undertaken. Initially, YAC cloning technology was employed to accomplish the required cloning. This proved only partially successful and ultimately unnecessary. X cloning, genomic southern analysis and transcriptional studies were employed to define the extent of the 1.22 metacyclic domain. The metacyclic domain was found to end 21 kb upstream of the 1.22BC gene. Sequence upstream of the metacyclic domain appears to be diploid and transcriptionally active, especially in metacyclic-derived trypanosomes. A gene candidate in this region was partially sequenced and found to have sequences highly homologous to a gene, ESAG 1, that occurs in bloodstream VSG gene expression sites