sentence: These results establish that NPr can be phosphorylated by other pathways ( possibly carbohydrate phosphotransferase systems ) when EI , EIIA , and SixA are absent and further establish that SixA does not require EI and EIIA to modulate NPr phosphorylation.We also tested whether SixA 's active-site histidine is required for the protein to affect NPr phosphorylation by comparing the effects of expressing wild-type SixA or a SixA ( H8A ) mutant .