MICRONUCLEAR RNA SYNTHESIS IN PARAMECIUM CAUDATUM

Abstract

A B S T R A C TIn a gcncration time of 8 hr in Paramecium caudatum, the bulk of D N A synthesis detected by thymidine-3H incorporation takes place in the latter part of the cell cycle. The micronuclear cycle includes a G1 of 3 hr followed by an S period of 3 -3~ hr. G2 and division occupies the remaining period of the cycle. Macronuclear R N A synthesis detected by 5'-uridine-3H incorporation is continuous throughout the cell cycle. Micronuclear R N A synthesis is restricted to the S period. Ribonuclcase removes 80-90 % of the incorporated label. Pulsc-chasc experiments showed that part of the R N A is conserved and releascd to the cytoplasm during the succecding G1 period.

STUDIES ON NUCLEAR STRUCTURE AND FUNCTION IN TETRAHYMENA PYRIFORMIS

“…Similar studies have been briefly reported by Alfert and Das (1959) . The results obtained here are compared with recent radioautographic studies of RNA synthesis in micronuclei of Paramecium caudatum (Rao and Prescott, 1967) and Paramecium aurelia (Pasternak, 1967) .…”

“…Studies similar to these have been performed in a related ciliate, Paramecium . Rao and Prescott (1967) labeled synchronized Paramecium caudatum with tritiated uridine for 30 min, isolated nuclei by using Triton X-100 plus spermidine (Prescott et al ., 1966), and made radioautography of the isolated nuclei . They found that micronuclei labeled with approximately one-tenth the intensity of macronuclei .…”

“…VOLUME 42, 1969 which it has been estimated that only one gene product per cell is sufficient to do so (Gibson and Beale, 1962) . Therefore, although it appears that micronuclei of Paramecium are capable of RNA synthesis (Rao and Prescott, 1967 ;Pasternak, 1967), the genes which have so far been introduced into micronuclei have no detectable function .…”

Indispensable function of the germ nucleus for postconjugational stomatogenesis inParamecium caudatum: Evidence against its genic function shown by hypohaploid micronuclei

“…In the Paramecium aurelia species complex, Pasternak [1967] reported that a small amount of RNA was synthesized in the micronucleus. In P. caudatum, there is no evidence of transcriptional activity during conjugation, although RNA synthesis in micronuclear S was reported [Rao and Prescott, 1967]. Nevertheless, there is strong evidence of micronuclear functioning during conjugation.…”

Characterization and Taxonomic Validity of the Ciliate Oxytricha trifallax (Class Spirotrichea) Based on Multiple Gene Sequences: Limitations in Identifying Genera Solely by Morphology

“…Like most ciliates, O. trifallax contains two types of nuclei: a somatic macronucleus (MAC) and a germline micronucleus (MIC). The MIC participates in sexual conjugation, but is otherwise transcriptionally silent (Narasimharao and Prescott 1967). During conjugation, O. trifallax destroys approximately 95% of its MIC genome and reorganizes the remaining pieces to generate over 20,000 highly processed MAC chromosomes, or nanochromosomes, typically bearing only a single gene (Prescott 2000; Swanton et al 1980).…”