The genomic clone hC3.11, isolated in 1989 in our laboratory encompasses the majority of the PSG-11 gene and contains 8.5 kb of upstream intergenic sequence. Nucleotide sequence from the initial 1.5 kb of the hC3.11 clone revealed the presence of a number of unique PSG-like C domains upstream of the PSG-11 gene. In this investigation, the sequencing of this region was completed resulting in 3.8 kb of contiguous sequence representing the area of interest. When compared to known PSG sequences the combined hC3.11 sequence was found to be similar to other PSG genes, but also contained several unique and previously unreported C-domain-like regions.
Chromosome walking techniques were used to investigate the area upstream of the PSG-11 gene. Two cosmid clones, #1 and #4, were isolated from a human genomic DNA library as potential candidates representing the a full length gene upstream of PSG-11. These were characterised by restriction enzyme mapping, cos-mapping and hybridisation analysis. Analysis of the data of these cosmid clones indicate that one of the clones represents an allelic variant of the hC3.11 region, whereas the other clone appears to contain a genomic fragment from another PSG locus.
Hybridisation analysis of the region stretching 9 kb upstream of the C-domain region of the hC3.11 clone failed to identify other PSG-related sequence. The absence of a PSG gene associated with the C-terminal domains, suggested that the hC3.11 C-domain region may be a remnant of evolutionary activity. It is proposed that the hC3.11 C-domain cluster represents a free-standing C-domain 'cassette', which may be ubiquitous amongst PSG gene family members.