The chlorarachniophyte: a cell with two different nuclei and two different telomeres

Chlorarachniophyte algae contain a complex chloroplast derived from the endosymbiosis of a eukaryotic alga. The reduced nucleus of the endosymbiont, the nucleomorph, is located between the inner and outer pair of membranes surrounding the chloroplast. The nucleomorph of chlorarachniophytes has previously been demonstrated to contain at least three small linear chromosomes. Here we describe cloning the end of the smallest nucleomorph chromosome which is shown to carry a telomere consisting of a tandemly repeated 7 bp sequence, TCTAGGG. Using the telomere repeat as a probe, we show that nucleomorph telomeres display typical hetero-disperse size distribution. The nucleomorph is shown to contain only three chromosomes with a haploid genome size of just 380kb. All six nucleomorph chromosome termini are identical with an rRNA cistron closely linked to the telomere. The nucleomorph chromosomes thus have relatively large inverted repeats at their ends. Chromosomes from the host nucleus are shown to have a different telomere repeat motif to that of the nucleomorph chromosomes.     

Absorption cytophotometry: Evaluation of three methods for the determination of DNA in feulgen stained nuclei

Summary Three methods for the evaluation of the relative amount of DNA per nucleus by absorption cytophotometry are compared. A combination of the two-wavelength method (Patau, 1952; Ornstein, 1952), the one-wavelength two-area method (Garcia, 1965) and the determination of transmission through nuclear plugs, is proposed in order to estimate systematic errors made by absorption cytophotometry.     

Absorption cytophotometry: evaluation of three methods for the determination of DNA in Feulgen stained nuclei.

Three methods for the evaluation of the relative amount of DNA per nucleus by absorption cytophotometry are compared. A combination of the two-wavelength method (Patau, 1952; Ornstein, 1952), the one-wavelength two-area method (Garcia, 1965) and the determination of transmission through nuclear plugs is proposed in order to estimate systematic errors made by absorption cytophotometry.     

RNA metabolism in nuclei: selective transport of kappa exons from myeloma nuclei and adenoviral transcripts from infected HeLa nuclei.

Two independent systems and several analytical procedures have been used to establish that isolated mammalian nuclei selectively transport mature RNA polymerase I and II products. Murine myeloma nuclei retain physiologic restriction in our transport assay as assessed by the transport of the immunoglobulin kappa light chain mRNA and 18S and 28S rRNAs. Nearly 50% of the total kappa exons are transported as structurally intact mature mRNA molecules while less than 8% of either pulse-labeled or steady state kappa intron sequences are detected in the transported fraction. Ribosomal external transcribed spacer sequences also are absent in transported RNA. Release of cytoplasmic RNA from the outer nuclear membrane during the transport assay accounts for less than 10% of transported RNA. Nuclei isolated from adenovirus-infected HeLa cells at 20 hours post infection retain cellular actin mRNA and transport viral poly A+RNA. Ribosomal RNA is transported from infected nuclei although at a reduced rate compared to transport from mock-infected nuclei. Inhibition of transport of host mRNA is paralleled by the absence of pulse-labeled actin mRNA in the cytoplasm of infected cells. The implications of our transport data in relationship to intranuclear RNA trafficking are discussed.     

Absorption and circular dichroism spectra of different forms of mushroom tyrosinase.

The circular dichroism spectrum of resting mushroom tyrosinase between 800 and 400 nm showed two bands at 755, and 653 nm. The CD spectrum of resting tyrosinase between 400 and 250 nm showed oxygen-sensitive changes at 350 nm upon treatment of tyrosinase with hydroxylamine or hydrogen peroxide. These were similar to changes observed on regeneration of aged hemocyanin by similar procedures. A structural relationship between the active sites of hydroxylamine- or hydrogen peroxide-treated tyrosinase and hemocyanin is suggested by these observations, confirming inferences based upon other studies (Jolly, Jr., R.L., Evans, L.H., Makino, N. and Mason, H.S. (1974) J. Biol. Chem. 249, 335-345 and Schoot Uiterkamp, A.J.M. and Mason, H.S. (1973) Proc. Natl. Acad, Sci. U.S. 70, 993-996).     

E. coli RNA polymerase interacts homologously with two different promoters

We present and review experiments that identify points of close approach of the RNA polymerase to two promoters, lac UV5 and T7 A3. We identify the contacts to the phosphates along the DNA backbone, to the N7s of guanines in the major groove and the N3s of adenines in the minor groove, and to the methyl groups of thymines. These contacts to the two promoters are strikingly homologous in space, as shown on three-dimensional models, and identify major regions of interactions lying on one side of the DNA molecule (at -35 and -16), as well as further areas extending through the Pribnow box. Both promoters are unwound similarly by the polymerase, across a region of about twelve bases extending from the middle of the Pribnow box to just beyond the RNA start site. We discuss the areas of interaction in the context of promoter homologies and promoter mutations. The disposition of the contacts in space suggests a model for the pathway along which the RNA polymerase binds to promoters.