Genes encoding the major surface glycoprotein in Leishmania are tandemly linked at a single chromosomal locus and are constitutively transcribed.

The major surface glycoprotein of Leishmania, gp63, is encoded by a small multi-gene family of tandemly linked genes which map to a single chromosome. For Leishmania major, there are five 3.1 kilobasepair (kb) direct repeat units which include a 1.8-kb open reading frame and a 1.3-kb intergenic or spacer region. In addition, there is a single gene copy linked as a direct repeat but separated from the tandem array of gp63 genes by about 8 kb. The restriction enzyme map of the repeat unit is highly conserved among the gene copies. The regions which flank the tandemly repeated genes diverge outside of the 3.1-kb repeat unit. Transcription of the gp63 gene locus is constitutive as the 3-kb transcript was present in promastigotes as well as in amastigotes. A minor 6-kb gp63 gene transcript was also detected in Northern blot analysis which could signify the transcription of the genes as a polycistronic or multigene precursor RNA.