The Endocommensal Ciliates of Venezuelan Sea Urchins

SYNOPSIS. Two hundred and fifty-nine specimens of the sea urchins Echinometra lucunter (201), Diadema antillarum (52), Tripneustes ventricosus (5) and Eucidaris tribuloides (1), collected on the littoral of the Federal District of Venezuela, were examined for intestinal ciliates.
Iron hematoxylin and silver-impregnation staining technics permitted determination of eight of the nine ciliates found: Anophrys aglycus, A. elongata, Cohnilembus caeci, Biggaria bermudensis, B. echinometris, Cyclidium rhabdotectum, Metopus circumlabens and M. rotundus . An unidentified species of Euplotes was also found.     

Cochlodinium heterolobatum n.sp.: Structure and Some Cytophysiological Aspects*

SYNOPSIS. Structure and morphogenesis, and cytochemical data on Cochlodinium heterolobatum, a new species of unarmored dinoflagellate, were derived from living and fixed material from culture. C. heterolobatum is characterized by the torsion of the girdle which descends in a left-hand spiral 1.8 turns; the sulcus having a torsion of 0.8 turn; a sulcus loop in the epicone; a tongue-shaped lobe in the right hypocone; nucleus in the epicone; and a stigma in the left epicone. Trichocysts and behavior of the nucleus during typical and atypical divisions are described in cells from cultures of different ages. A small form with the specific characters was found. Intracellular bacteria were seen and their growth followed in individuals from cultures of different ages. A possible relationship between those bacteria and the accumulation of metabolites inside old cells is discussed.     

RECIPROCAL BEHAVIOR OF THE RACHIS AND PEDUNCLE IN COLONIES OF Veretillum cynomorium PALL.

Some integrated patterns of behavior have been studied in coloniesof Veretillum cynomorium, whose various parts often act as ifthey were those of an individual consisting of the whole colony.The entire colony is involved in slow rhythmical movements,in which phases of contraction alternate with expansion. Thisbehavior corresponds to a permanent reciprocity (or duality)between the zooid-bearing rachis and the peduncle; overall behavioris determined by the number of "functionally active units" whicheither contains at any given time. This number is influencedby the excitatory or restraining effects of external factorssuch as light intensity or the entry of water. In this way,when contraction proceeds, activity of the rachis predominates,whereas during swelling of the colony, activity of the peduncleprevails. Observations on intact colonies and on specimens without peduncles,experiments using light and electrical stimuli, and the studyof peristalsis, all suggest that the mutually reciprocal natureof activity in the rachis and peduncle may be attributed tothe differential influence of external factors on the functionalstate of centers of spontaneous activity or of conduction pathwaysin the colony. Zooids present on the rachis are responsibleboth for the reciprocal activity of the colony and for its morphologicalpolarity.     

The 15 N-terminal amino acids of hexokinase II are not required for in vivo function: analysis of a truncated form of hexokinase II in Saccharomyces cerevisiae

The function of the N-terminal amino acids of Saccharomyces cerevisiae hexokinase II was studied in vivo using strains producing a form of hexokinase II lacking its first 15 amino acids (short form). This short form of hexokinase II was produced from a fusion between the promoter region of the PGK1 gene and the HXK2 coding sequence except the first 15 codons. As expected, the in vitro analysis of the short form protein by gel filtration chromatography indicates that the short protein does not form dimers under conditions where the wild-type protein dimerizes. Kinetic studies show that the enzymatic activities are very similar to wild-type behavior. The physiological experiments performed on the strains containing the fusion allele demonstrate that the short form of the enzyme is similar to the wild-type both in terms of phosphorylation of hexoses and glucose repression. We conclude that the N-terminal amino acids of hexokinase II are not required in vivo either for phosphorylation of hexoses or for glucose repression.