MmuEX0030353 @ mm9

An isoform of non-muscle myosin II-C (NM II-C), called NM II-C2, is generated by inclusion of a casette exon, C2 (MmuEX0030353 in mouse, HsaEX0040957 in humans), encoding 41 amino acids in mice (33 amino acids in humans). The 41 amino acids are inserted into loop 2 of the NM II-C heavy chain within the actin binding region. Unlike most vertebrate non-muscle and smooth muscle myosin IIs, baculovirus-expressed mouse heavy meromyosin (HMM) II-C2 demonstrates no requirement for regulatory myosin light chain (MLC(20)) phosphorylation for maximum actin-activated MgATPase activity or maximum in vitro motility as measured by the sliding actin filament assay. In contrast, noninserted HMM II-C0 and another alternatively spliced isoform HMM II-C1, which contains 8 amino acids inserted into loop 1, are dependent on MLC(20) phosphorylation for both actin-activated MgATPase activity and in vitro motility. HMM II-C1C2, which contains both the C1 and C2 inserts, does not require MLC(20) phosphorylation for full activity similar to HMM II-C2. These constitutively active C2-inserted isoforms of NM II-C are expressed only in neuronal tissue. This is in contrast to NM II-C1 and NM II-C0, both of which are ubiquitously expressed. Full-length NM II-C2-GFP expressed in COS-7 cells localizes to filaments in interphase cells and to the cytokinetic ring in dividing cells.