It may identify MTAP (5′-deoxy-5′-methylthioadenosinephosphorylase), a 31 kDa protein. It catalyses the reversiblephosphorolysis of methylthioadenosine, which is crucial forthe salvage of methionine and adenine as well aspolyamine metabolism. The tumour suppressor gene,p16INK4A, is connected to the gene that codes for MTAP.Co-deletion of the MTAP gene and the p16INK4A gene isthe main way that tumours can have low amounts of MTAP.The growth-inhibitory effects of drugs (such as antifolates),whose mechanism of action partially involves this de novopurine pathway, may make cells expressing MTAP andhaving adenine salvage pathway activity less prone tocancer.