We investigated the expression of the α subunit of the Dictyostelium mitochondrial 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, designated α-MPPH and α-MPPL, throughout the Dictyostelium life cycle. The larger form, α-MPPH, is cleaved to produce the functional α-MPPL form. We were not able to isolate mutants in which the α-mpp gene had been disrupted. Instead, an antisense transformant, αA2, expressing α-MPP at a lower level than the wild-type AX-3 was isolated to examine the function of the α-MPP protein. Development of the αA2 strain was normal until the slug formation stage, but the slug stage was prolonged to ∼24 h. In this prolonged slug stage, only α-MPPH was present, and α-MPPL protein and MPP activity were not detected. After 28 h, α-MPPL and 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 of α-MPPH to α-MPPL during development in Dictyostelium.
Mitochondrial processing peptidase activity is controlled by the processing of α-MPP during development in Dictyostelium discoideum