Phosphorylation of the major Drosophila lamin in vivo: Site identificationduring both M-phase (meiosis) and interphase by electrospray ionization tandem mass spectrometry

Phosphorylation can have profound effects on the properties of nuclear lami ns. For instance, phosphorylation of specific sites on mammalian lamins dra stically alters their propensity to polymerize. Relatively little is known about the effects of phosphorylation during interphase and about phosphoryl ation of invertebrate nuclear lamins. Here, using electrospray ionization t andem mass spectrometry, we determined the phosphorylation sites of both in terphase and M-phase isoforms of nuclear lamin Dm from Drosophila melanogas ter. Interphase lamins are phosphorylated at three sites: two of these site s (Ser(25) and a site located between residues 430 and 438) flank the alpha -helical rod domain, whereas the third site (Ser(595)) is located close to the C-terminus. The M-phase lamin isoform is phosphorylated predominantly a t Ser(45), a residue contained within a sequence matching the consensus sit e for phosphorylation by cdc2 kinase. Our study confirms the important role in vivo for cdc2 kinase in M-phase disassembly of nuclear lamins and provi des the basis for understanding Drosophila lamin phosphorylation during int erphase.