PHOSPHOGLYCERATE KINASE PSEUDOGENES IN THE TAMMAR WALLABY AND OTHER MACROPODID MARSUPIALS

Phosphoglycerate kinase (EC 2.7.2.3; PGK) exists in two forms in marsu pials. PGK1 is an X-linked house-keeping enzyme, and PGK2 is a mainly testis-specific enzyme under autosomal control. We have used PGK1 prob es derived from two closely related species of macropodid marsupials ( kangaroos and wallabies) to demonstrate the existence of a large famil y of pseudogenes in the tammar wallaby (Macropus eugenii). Over 30 fra gments are detectable after Tag digestion. We estimate that there are 25-30 copies per genome. Most are autosomally inherited and are appare ntly not closely linked. Only two restriction fragments that appeared to be sex linked could be detected. Varying degrees of hybridization o f fragments to the probes suggest different levels of homology, and he nce different ages of origin. The existence of two PGK1 homologous res triction fragments from the X and a large number from the autosomes wa s also demonstrated by somatic cell hybridization for two other macrop odid species, the wallaroo (M. robustus) and the red kangaroo (M. rufu s). These results are compared with those from human and mouse, and it is suggested that the propensity of PGK1 to form pseudogenes is an an cient (similar to 130 MYR BP) characteristic of mammals. The high leve l of polymorphism detected in the tammar makes these PGK1 probes poten tially useful for measuring genetic variability in this species and ot her macropodids.