Phosphomethylpyrimidine kinase (<db_xref db="EC" dbkey="2.7.4.7"/>), also known as HMP-phosphate kinase, catalyses the phosphorylation of HMP-P to HMP-PP in the reaction: ATP + 4-amino-2-methyl-5-phosphomethylpyrimidine = ADP + 4-amino-2-methyl-5-diphosphomethylpyrimidine during the biosynthesis of thiamine.