Mitochondrial processing peptidase activity is controlled by the processing of α-MPP during development in Dictyostelium discoideum

Abstract

We investigated the expression of theαsubunit of theDictyosteliummitochondrial processing peptidase (Ddα-MPP) during development. Ddα-MPP mRNA is expressed at the highest levels in vegetatively growing cells and during early development, and is markedly downregulated after 10 h of development. The Ddα-MPP protein is expressed as two forms, designatedα-MPPHandα-MPPL, throughout theDictyosteliumlife cycle. The larger form,α-MPPH, is cleaved to produce the functionalα-MPPLform. We were not able to isolate mutants in which theα-mppgene had been disrupted. Instead, an antisense transformant,αA2, expressingα-MPP at a lower level than the wild-type AX-3 was isolated to examine the function of theα-MPP protein. Development of theαA2 strain was normal until the slug formation stage, but the slug stage was prolonged to ∼24 h. In this prolonged slug stage, onlyα-MPPHwas present, andα-MPPLprotein and MPP activity were not detected. After 28 h,α-MPPLand MPP activity reappeared, and normal fruiting bodies were formed after a delay of approximately 8 h compared with normal development. These results indicate that MPP activity is controlled by the processing ofα-MPPHtoα-MPPLduring development inDictyostelium.