The interaction of metastatic cells with their environment is mediated to a large extent by the cell surface. Although several biochemical differences between tumour cells with low or high metastatic potentials have been reported, the specific surface characteristics associated with metastasis have not yet been identified. One distinctive feature of murine B16 melanoma variants with low (B16-F1, B16-F10Lr) or high (B16-F10) lung colonisation potentials is their propensity to aggregate in vitro with other tumour cells (homotypic clumping), or with host cells (heterotypic clumping). The initial sites for membrane-membrane recognition, contact and subsequent interaction are thought to be associated with dense membrane anionic sites. In the experiments reported here we determined that the distribution of cell-surface dense anionic sites, examined ultrastructurally with the use of cationised ferritin (CF), is correlated with tumour cell aggregation in vitro and/or production of pulmonary tumour colonies following intravenous (i.v.) injection into syngeneic recipients.

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The PR-factor, an enzyme necessary for the production of protoplasts from yeast, was identified and was named phosphomannanase. The enzyme released mannan and mannan-proteins from yeasts harvested in the logarithmic phase of growth. The size of the molecules released was greater than 200,000 daltons, which indicated that the enzyme splits very few bonds of the yeast wall. The PR-factor also depolymerized phosphomannans produced by the Hansenula species. The degradation of these substances was due to the splitting of mannosidic bonds. However, the phosphodiester bonds present in these phosphomannans were involved in the specificity of the enzyme, and the number of mannosidic bonds cleaved was dependent on the number of phosphodiester bonds present. We studied the products of degradation of Hansenula phosphomannans and were unable to identify the exact bond split by the enzyme. After enzymatic digestion and subsequent splitting of phosphodiester bonds, phosphomannan Y-2448 yielded products too complex to be separated. Phosphomannan Y-1842 was shown to have a structure more complex than that previously proposed. The action of the enzyme on the phosphate-rich walls of Saccharomyces was studied. Mannan, containing intact phosphodiester bonds, was released from the walls. Mild acid hydrolysis of this released material split the diester bonds to yield monosaccharide and polysaccharide terminated in mannose-6-phosphate. From these products, we deduced that the enzyme cleaved a mannosidic bond adjacent to a mannose, which is also phosphodiester linked through carbon 1. The significance of phosphodiester bonds in the attachment of mannan and mannan-protein enzymes to the wall of yeast is discussed.

Abstract. Translation of bacterial mRNA, divorced from transcription, has been obtained for enzymes of arginine synthesis; evidence has been acquired for repression by arginine at the level of translation. mRNAs Translational models for the regulation of the synthesis of arginine enzymes have been considered since the development of the repression concept.'-5 By and large, though, the idea of translational regulatory mechanisms in bacteria has recently received relatively little attention, perhaps because of the demonstration of transcriptional control through gene-affined repressors in such intensively studied cases as that of the Lac system in Escherichia coli.6 Nevertheless, translational repression has remained an attractive possibility for enzymes of bacterial amino acid synthesis and possibly for a broader spectrum of proteins (see ref. 7).In the present experiments, the formation of mRNA has been separated from its translation, and a reduction in translation under repressive conditions has been demonstrated.Materials and Methods. Strains: The organisms used are related to strain 619 (his-ile-met-), a derivative of E. coli K12 (ref. 8). Strain 961 (argR+) is an arginine auxotroph derived from strain 619 (refs. 9, 10) and strain 977 (argR-, ref. 10) is a his+ recombinant of strain 961, which had received the argR-gene from the Hfr strain 3134 (ref. 8). The arginine auxotrophy of these two strains is caused by a mutation that maps in the region of the four-gene cluster of the arginine system and is pleiotropic, affecting the level of three out of the four enzymes specified by the clustered genes.10 The auxotrophs do not grow without an added arginine source, but grow at the wild-type rate on minimal medium supplemented with arginine (and the other required 1703