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A buffer system conitainin chloral hydrate, taurine, and bromopyridinium lactate was used to dissolve several biological membranes and separate their protein components by polyacrylamide gel electrophoresis. This solvent system was capable of separating molecules of similar size on the hasis of their charge and allows easy recovery of the proteins Thus. aqueous chloral hydrate is an effective solvent for biological membranes.

A dialysable low-molecular-weight factor capable of affecting in vitro properties of macrophages was extracted from four different mouse tumors. This factor not only modulates closely related properties of peritoneal macrophages such as spreading and migration but also inhibits lipopolysaccharde-induced tumoricidal activity of these cells. It can be extracted not only from tumor tissues but also from tumor cells grown in vitro. The appearance of this factor is unique to tumors and it is not present in detectable quantities in normal tissues. The factor from one of the tumors, Lewis lung carcinoma, was purified extensively and the partially purified factor retains all the above effects on macrophages. It is not sensitive to pronase or a mixture of bovine spleen phosphodiesterase II, E. coli alkaline phosphatase and pancreatic ribonuclease. The factor is lipid-like in character and it is soluble in both organic solvents and aqueous media. It has ionizable group(s) and is anionic at neutral pH but non-ionic under acidic conditions.

The translation of a sequence of codons (in messenger RNA) into an amino acid sequence (in protein) is mediated by various species of aminoacyl-tRNA's.-1 2 There is evidence for the view that each transfer RNA species has a specific region whose nucleotide sequence is complementary to those of the codons specifying the aminoacyl residue attached to the transfer RNA. This region is designated as the anticodon.2-4 Unambiguous translation depends on correct matching of the anticodons in aminoacyl-tRNA's to codons in messenger RNA. The esterification of amino acids to transfer RNA's is catalyzed by aminoacyl-tRNA synthetases. Each enzyme in this category appears to be specific for one amino acid.2 It is an obvious question whether the anticodon (which determines the specificity of aminoacyl-tRNA in the translation process) is also the specific recognition site for the aminoacyl-tRNA synthetase. One approach to this problem was to modify tRNA (e.g., by irradiation, by chemical treatment, or by genetic manipulation) and to test the effect of this modification upon the ability of the transfer RNA to be charged.2 4 Although several earlier experimental results were interpreted in favor of the anticodon serving as the recognition site for aminoacyl-tRNA synthetase,2 4 more recent studies seem to contradict this. They suggest that alteration of a single nucleotide in the anticodon5-8 or cleavage of a phosphodiester linkage in the anticodon9 do not abolish the ability of the transfer RNA to be aminoacylated.We based our study on the following facts and considerations. Cases exist in which the same kind of amino acid may be attached to different transfer RNA species (isoaccepting transfer RNA's).2 There are experiments indicating that certain isoaccepting transfer RNA's can be charged by the same aminoacyl-tRNA synthetase.10' 11 Various isoaccepting transfer RNA's frequently respond to different codons.12 In most cases, such codons differ only in one nucleotide and have two nucleotides in common. A unique possibility is provided by the occurrence in E. coli of two tRNASer species that respond to codons with entirely unrelated nucleotide sequences: tRNASer Ila, to AGU and AGC; tRNAser Ilb, to UCA and UCG.13 It is presumed that the nucleotide sequences of the anticodons in these two tRNASer species are also unrelated. Consequently, if both species were recognized by the same ser-tRNA synthetase, it would follow that it is not the anticodon which serves as a specific recognition site for the enzyme. In this communication, we present results indicating that tRNAser Ila and tRNASer Ilb are charged by the same ser-tRNA synthetase.Materials and Methods.-ApG, UpC, C4-L-serine (112 jgc/umole) and H'-iserine (3.73 mc/,mole) were commercial products. Polynucleotide phosphorylase from Micrococcus 693