Kenneth C. Holmes

Structure of Tobacco Mosaic Virus at 6.7 A Resolution

The electron density distribution of tobacco mosaic virus has been determined to 6.7 Å resolution by analysis of the X-ray diffraction pattern given by oriented gels of the virus. This has been achieved by separation of overlapping Bessel function terms by a technique analogous to crystallographic isomorphous replacement. The course of the polypeptide chain of the coat protein may be traced for a large part of its length.

The radial density distribution in some strains of tobacco mosaic virus

Abstract The radial electron density distribution in four strains of tobacco mosaic virus (TMV) and in cucumber virus 4 (CV4) has been calculated. It is found that the principal structural features of TMV are common to all strains: the virus particles all have a hollow core of radius about 20 A, a maximum radius of about 90 A, a high density peak due to nucleic acid at a radius of 40 A, and prominent peaks in protein density at 24 A, 66 A, and 78 A. Further, in all strains the helical array of protein subunits bears 49 subunits in every three turns. The strains differ from one another principally in the relative heights of the peaks in protein density; that is, in the weights of protein lying at particular radii.

A new helical aggregate of Tobacco Mosaic Virus Protein

Tobacco mosaic virus coat protein has been repolymerized in the absence of RNA and investigated by X-ray analysis. The rods obtained can be classified in two different helical surface lattices (class A and B), having nearly 16 1/3 and 17 1/3 subunits per turn, respectively, with only small differences in polypeptide chain folding. The structure of the protein rod in helix class A is almost identical with that in intact tobacco mosaic virus, while in the absence of the RNA the class B surface lattice is predominant.

X−ray diffraction studies of concentrated gels of ribosomes from E.coli

X-ray diffraction patterns showing 9 maxima at spacings greater than 10 A have been obtained from concentrated gels of E. coli 50 s ribosomes. The observed spacings can be fitted to integral orders of 212 A basic repeat, with the exception of a reflection at 45·5 A. It is suggested that both the 50 s and 70 s particles form a linear polymer in the concentrated gel with a repeat spacing of 212 A. The 45·5 A reflection is believed to arise from some internal structure in the ribosome.

The positions of the N-terminus and residue 68 in tobacco mosaic virus

Abstract Specific chemical modifications of the tobacco mosaic virus coat protein lead to new heavy-atom derivatives. They can be used for the determination of phases in the isomorphous replacement method, but more important they are necessary as markers if one wants to trace the polypeptide chain through an electron density map of limited resolution (10 A). In addition to the positions of two residues known from previous work, two more residues out of the 158 have now been located in three dimensions. The N-terminus is at the outside of the particle ( r = 88 A), and Lys-68 lies at a radius of 72 A.

Molecular structure of the actomyosin system in cross striated muscle

The present dogma of muscle contraction is founded principally on two tenets: (1) that contraction is the result of an interaction between actin, myosin and adenosine triphosphate (ATP), and (2) that contraction proceeds by a sliding mechanism which does not involve permanent change in the length or configuration of the component protein molecules. Actomyosin is an ATPase needing Mg++ ion as a co-factor but not Ca++ ion. The Ca++ concentration on the other hand plays a vital role in switching the muscle from a resting to an active state. I wish to acknowledge at the outset the debt we owe to Dr. H. E. Huxley for his unique role in the development of the structural ideas underlying this hypothesis.