The Journal of Cell Biology, Vol 100, 1799-1804, Copyright © 1985 by The Rockefeller University Press

ARTICLES

Slow posttranslational modification of a neurofilament protein

GS Bennett and C DiLullo

The synthesis and subsequent modification of neurofilament (NF) polypeptides has been examined in pulse-chase experiments, using cultured chick spinal cord neurons. Fluorography of the [35S]methionine- labeled cytoskeletal proteins, after separation by two-dimensional gel electrophoresis, revealed that (a) the mid-size chicken NF protein, NF- M160, is synthesized as a smaller and more basic precursor, NF-M130; (b) beginning approximately 8 h after translation, NF-M130 slowly and continuously becomes larger and more acidic, attaining the size and charge of NF-M160 16 or more h later, and undergoing no further change in mobility for many days thereafter; and (c) in contrast, the low molecular weight NF protein, NF-L, is synthesized as such, and undergoes no subsequent change in apparent size or charge. Additional experiments provided evidence that the conversion of NF-M130 to NF-M160 is due, at least in part, to phosphorylation: (a) Incubation of similar cultures in 32PO4 resulted in incorporation into NF-M160 and transitional forms, but not into NF-M130. (b) An antiserum to NF-M160 was found by immunoblot analysis to bind strongly to untreated NF-M160, but poorly to phosphatase-treated NF-M160, and not at all to NF-M130. It has already been demonstrated (Bennett, G. S., S. J. Tapscott, C. DiLullo, and H. Holtzer, 1984, Brain Res., 304:291-302) that this anti- NF-M160 fails to stain the soma of motor neurons in sections of chick spinal cord, but detects an increasing gradient of immunoreactivity in the proximal axons. These results, together with the known kinetics of axoplasmic transport of NF, suggest that the mid-size chicken NF protein is synthesized as NF-M130 and is extensively modified, at least in part by phosphorylation, to become NF-M160 during transport along proximal neurites. Once maximally modified, NF-M160 undergoes no further net change during transport along distal neurites.
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This article has been cited by other articles:

• Brown, A (1998). Contiguous phosphorylated and non-phosphorylated domains along axonal neurofilaments. J. Cell Sci. 111: 455-467 [Abstract]  
• Zopf, D, Hermans-Borgmeyer, I, Gundelfinger, E D, Betz, H (1987). Identification of gene products expressed in the developing chick visual system: characterization of a middle-molecular-weight neurofilament cDNA.. Genes Dev. 1: 699-708 [Abstract]  

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