We have studied the effect of the drug pactamycin on protein synthesis in poliovirus-infected HeLa cells. At a concentration which primarily inhibits initiation of protein synthesis, the spectrum of poliovirus proteins synthesized is markedly changed. The amount of NCVP 1, the capsid precursor, is greatly reduced relative to NCVP 2 and the amount of NCVP X is slightly reduced. Since it is believed that there is only one major site for the initiation of protein synthesis on the poliovirus genome, we interpret this differential effect on the poliovirus proteins to be an indication of their relative distance from the initiation site. On this basis, we propose a gene order for the poliovirus genome (5'-* 3') of NCVP 1, NCVP X, NCVP 2.

The molybdenum- and iron-containing protein components of nitrogenase purified from Klebsiella pneumoniae, Azotobacter vinelandii, Azotobacter chroococcum and Rhizobium japonicum bacteroids all gave either one or two protein-staining bands after sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, depending on the commercial brand of sodium dodecyl sulphate used. The single band obtained with K. pneumoniae Mo-Fe protein when some commercial brands of sodium dodecyl sulphate were used in the preparation of the electrode buffer was resolved into two bands by the addition of 0.01% (v/v) dodecanol to the buffer. Protein extracted from the two bands obtained after electrophoresis of K. pneumoniae Mo-Fe protein gave unique and distinct peptide 'maps' after tryptic digestion. Undissociated Mo-Fe protein contained both sets of tryptic peptides. These data are consistent with Mo-Fe protein from K. pneumoniae being composed of non-identical subunits. Amino acid analyses of the subunit proteins revealed some clear differences in amino acid content, but the two subunits showed close compositional relatedness, with a different index [Metzer, H., Shapiro, M.B., Mosiman, J.E. & Vinton, J.G. (1968) Nature (London) 219, 1166-1168] of 4.7.

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