The population dynamics of young trout (Salmo trutta L.) in a Danish brook

The population size, dispersal of fry, growth of fry in relation to density, mortality and production of young trout ( Salmo trutta L.) were studied in a Danish brook during 1970–1972. In the first few months after emergence downstream emigration of fry took place both in 1971 and 1972, after which the trout became stationary. Growth was inversely density dependent and mortality was density dependent in the months just after emergence. Later mortality was constant and independent of density. Trout production varied between 10 g/m² and 18.6 g/m² in the 2 years.     

Tandem translation of Bacillus subtilis initiation factor IF2 in E. coli. Over-expression of infBB.su in E. coli and purification of alpha- and beta-forms of IF2B.su.

The protein synthesis initiation factor, IF2, in Bacillus subtilis has previously been characterized as being present in two forms, alpha and beta, of molecular mass 79 and 68 kDa, respectively, on the basis of their cross-reaction with anti-E. coli IF2 antibodies and by the DNA sequence of the gene for IF2, infBB.su. In this work we have cloned infBB.su in E. coli cells. Two proteins of molecular mass identical to the B. subtilis IF2 alpha and -beta were over-expressed and purified using a new three-step ion-exchange chromatography procedure. The N-terminal amino acid sequence of the two proteins was determined and the results confirmed that the two forms were IF2 alpha and -beta, both encoded by the infB gene. The N-terminal amino acid sequence determined for IF2 beta is Met94-Gln-Asn-Asn-Gln-Phe. The presence of methionine at position 94 shows that this form is, in fact, the result of a second translational initiation in infBB.su mRNA, since the codon at amino acid position 94 is GUG, which is the normal codon for valine, but also known to be an initiator codon. This is a new example of the unusual tandem translation in E. coli of an open mRNA reading frame.     

Biochemical investigations of retinotectal adhesive specificity

The preferential adhesion of chick neural retina cells to surfaces of intact optic tecta has been investigated biochemically. The study uses a collection assay in which single cells from either dorsal or ventral halves of neural retain adhere preferentially to ventral or dorsal halves of optic tecta respectively. The data presented support the following conclusions: (a) The adhesion of ventral retina to dorsal tecta seems to depend on proteins located on ventral retina and on terminal β-N-acetylgalactosamine residues on dorsal tecta. (b) The adhesion of dorsal retina to ventral tecta seems to depend on proteins located on ventral tecta and on terminal β- N-acetylgalactosamine residues on dorsal retina. (c) A double gradient model for retinotectal adhesion along the dorsoventral axis is consistent with the data presented. The model utilizes only two complementary molecules. The molecule suggested to be concentrated dorsally in both retina and tectum seems to require terminal β-N-acetylgalactosamine residues for adhesion. Its activity is not affected by protease. A molecule fitting these qualifications, the ganglioside GM(2), could not be detected in a gradient, but lecithin vesicles containing GM(2) adhered preferentially to ventral tectal surfaces. The second molecule, concentrated ventrally in both retina and tectum, is a protein and seems capable of binding terminal β-N- acetylgalactosamine residues. One enzyme, UDP-galactose:GM(2) galactosyltransferase, has been found to be more concentrated in ventral retina than dorsal, but only by 30 percent.