Intermediate filaments exchange subunits along their length and elongate by end-to-end annealing.
Actin filaments and microtubules lengthen and shorten by addition and loss of subunits at their ends, but it is not known whether this is also true for intermediate filaments. In fact, several studies suggest that in vivo, intermediate filaments may lengthen by end-to-end annealing and that addition and loss of subunits is not confined to the filament ends. To test these hypotheses, we investigated the assembly dynamics of neurofilament and vimentin intermediate filament proteins in cultured cells using cell fusion, photobleaching, and photoactivation strategies in combination with conventional and photoactivatable fluorescent fusion proteins. We show that neurofilaments and vimentin filaments lengthen by end-to-end annealing of assembled filaments. We also show that neurofilaments and vimentin filaments incorporate subunits along their length by intercalation into the filament wall with no preferential addition of subunits to the filament ends, a process which we term intercalary subunit exchange.
Colakoğlu
Gülsen
G
Center for Molecular Neurobiology, The Ohio State University, Columbus, OH 43210, USA.
Brown
Anthony
A
D002460:Cell Line; D002478:Cells, Cultured; D049452:Green Fluorescent Proteins / Q000032:analysis; D006801:Humans; D007382:Intermediate Filaments / Q000378:metabolism* / Q000648:ultrastructure; D008954:Models, Biological; D016900:Neurofilament Proteins / Q000032:analysis / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000032:analysis; D014746:Vimentin / Q000032:analysis / Q000378:metabolism
D016900:Neurofilament Proteins; D011993:Recombinant Fusion Proteins; D014746:Vimentin; D049452:Green Fluorescent Proteins