In addition to protein quality control, evidence thatHsClpXP has regulatory roles in multiple biological pathwaysis accumulating. For example, it may participate in the negativefeedback mechanism for regulating heme biosynthesis by thedegradation of the mitochondrial 5-aminolevulinate synthaseALAS1 and the erythroid-specific ALAS2, both of whichmediate the first step in protoporphyrin IX biosynthesis