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© The Rockefeller University Press, 0021-9525/1999//1039 $5.00
The Journal of Cell Biology, Volume 147, Number 5, , 1999 1039-1048

Original Article

A Structural Model for Phosphorylation Control of Dictyostelium Myosin II Thick Filament Assembly



Wenchuan Lianga, Hans M. Warricka, and James A. Spudicha

a Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305-5307
Department of Biochemistry, Stanford University School of Medicine, Beckman Center, Stanford, CA 94305-5307.(650) 723-6783(650) 723-7634

jspudich{at}cmgm.stanford.edu

Myosin II thick filament assembly in Dictyostelium is regulated by phosphorylation at three threonines in the tail region of the molecule. Converting these three threonines to aspartates (3xAsp myosin II), which mimics the phosphorylated state, inhibits filament assembly in vitro, and 3xAsp myosin II fails to rescue myosin II–null phenotypes. Here we report a suppressor screen of Dictyostelium myosin II–null cells containing 3xAsp myosin II, which reveals a 21-kD region in the tail that is critical for the phosphorylation control. These data, combined with new structural evidence from electron microscopy and sequence analyses, provide evidence that thick filament assembly control involves the folding of myosin II into a bent monomer, which is unable to incorporate into thick filaments. The data are consistent with a structural model for the bent monomer in which two specific regions of the tail interact to form an antiparallel tetrameric coiled–coil structure.

Key Words: myosin II • thick filament assembly • Dictyostelium • phosphorylation • suppressor screen

© 1999 The Rockefeller University Press

Abbreviation used in this paper: NQNO, 4-nitroquinoline-N-oxide.


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