Lamin 501125 214647978 2008-05-24T16:04:31Z BartekChom 4437479 pl '''Lamins''' are [[fibrous protein]]s providing structural function and transcriptional regulation in the [[cell nucleus]]. They are also involved in the positioning of nuclear pores. ==A and B types== In [[metazoan]] cells there are A and B type lamins which differ in their length and [[Isoelectric point|pI]]. Human cells have three differentially regulated [[gene]]s. * B-type lamins are present in every cell. B type lamins, B1 and B2, are expressed from the [[LMNB1]] and [[LMNB2]] genes on 5q23 and 19q13, respectively. * A-type lamins are only expressed following [[gastrulation]]. Lamin A and C are the most common A-type lamins and are splice variants of the [[LMNA]] gene found at 1q21. ==Function and structure== These proteins localize to two regions of the [[cell nucleus|nuclear compartment]], the [[nuclear lamina]] -- a proteinaceous structure layer subjacent to the inner surface of the [[nuclear envelope]] and throughout the nucleoplasm in the nucleoplasmic "veil". Comparison of the lamins to vertebrate cytoskeletal IFs shows that lamins have an extra 42 residues (six heptads) within coil 1b. The c-terminal tail domain contains a [[nuclear localization signal]] (NLS), an Ig-fold like domain, and in most cases a carboxy-terminal CaaX box that is isoprenylated and carboxymethylated (lamin C does not have a CAAX box). Lamin A is further processed to remove the last 15 amino acids and its farnesylated cysteine. Lamin A and lamin C form homodimers which associate head to tail. During mitosis, lamins are phosphorylated by MPF which drives the disassembly of the lamina and the nuclear envelope. ==See also== * [[intermediate filament]] * [[nuclear lamina]] * [[laminopathies]] ==External links== * {{MeshName|Lamins}} {{Cytoskeletal Proteins}} [[Category:Structural proteins]] [[de:Lamin]] [[it:Lamina (proteina)]] [[pl:Laminy]] [[pt:Lamina]]