Transposition of the gene cluster CYC1-OSM1-RAD7 in yeast

A mutant of the yeast Saccharomyces cerevisiae contains an increased amount of iso-1-cytochrome c because two copies of a segment, denoted COR, were transposed to a new position on chromosome VII, while the original COR region was retained at the normal position on chromosome X; this COR segment encompasses the CYC1, OSM1 and RAD7 loci which determine, respectively, iso-1-cytochrome c, osmotic sensitivity and ultraviolet light sensitivity. The analysis of genomic DNA with cloned probes indicates that the length of the COR segment is approximately 12,000 base-pairs. We suggest that certain normal strains of yeast, which possibly may contain reiterated sequences, can produce extended transpositions similar to prokaryotes.     

3S,24S,25-Trihydroxytirucall-7-ene from Ailanthus excelsa

A new triterpene has been isolated from the root bark of Ailanthus excelsa (Simaroubaceae) and identified as 3S,24S,25-trihydroxytirucall-7-ene.     

Stimulation of differentiation of several murine embryonal carcinoma cell lines by retinoic acid

Retinoic acid stimulates several murine embryonal carcinoma (EC) cell lines, even those previously considered to be incapable of differentiating, to give rise to cell types distinguishable from the parental phenotype in morphology, production of plasminogen activator and surface protein properties. Retinoic acid promotes these changes over a range of low concentrations (10⁻⁹–10⁻⁵ M) which are generally non-toxic to the cells. The effects are clearly demonstrated when EC cells are aggregated prior to exposure to retinoic acid. It is concluded that the observed phenotypic alterations induced by retinoic acid reflect differentiation of the EC cells since non-EC cell characteristics are maintained by cloned cells several generations after retinoic acid is removed from the cultures. Our studies suggest that although retinoic acid stimulates the conversion of EC cells to differentiated derivatives, it does not influence the direction of differentiation. Furthermore, the effectiveness of retinoic acid in stimulating differentiation of EC cells from lines such as Nulli-SCC1 raises the question of whether true ‘nullipotent’ EC lines really exist.     

Development and differentiation of mouse blastocysts in serum-free medium

Numerous studies have shown that the in vitro development and differentiation of mouse blastocysts require serum, but the number and nature of serum factors involved remains unclear. In this article, we describe a culture medium, EM-2, containing as a source of protein only commercially purified bovine serum albumin (BSA) and fetuin. This medium supports hatching, attachment and outgrowth of mouse blastocysts. Although attachment and outgrowth are delayed in EM-2 medium 12–15 and 5–8 h, respectively, these events occur at frequencies comparable to those observed in serum-containing media. Trophoblast cells are capable of differentiating in this medium: they synthesize Δ⁵,3β-hydroxysteroid dehydrogenase and their nuclei become polyploid. The inner cell mass also appears to differentiate to some extent in EM-2 medium as evidenced by the appearance of cells with characteristics of parietal endoderm. The fetuin factor is necessary at least for trophoblast outgrowth and the albumin factor is required for the survival and/or growth of the inner cell mass. It is, however, not evident from these studies whether the serum fractions used are actually involved in the induction of differentiation, or whether the early differentiative steps in the mouse blastocyst are preprogrammed and require for expression only a normal cellular metabolic rate.     

Biopterin

An enzyme that catalyzes the conversion of 2-amino-6-(5'-triphosphoribosyl)amino-5- or 6-formamido-6-hydroxypyrimidine, but not of guanosine triphosphate, to quinonoid 6-(D-erythro-1'-2'-3'-trihydroxypropyl)dihydropterin triphosphate and formic acid has been purified to homogeneity from some mammalian brain and liver. The enzyme of a single strand is a basic protein of 9177 daltons consisting of 68 amino acid residues--except the enzyme from rat brain, which has one additional aspartic acid as residue 7. The enzyme possesses three free SH groups and, in its most active form, 1 mol of phosphate per mole of enzyme. Peptides isolated after hydrolysis with trypsin, chymotrypsin, or weak acid were separated by thin-layer chromatography and sequenced manually by Edman degradation. The complete sequence of the molecule was established as follows: (formula: see text)