Uridine phosphorylase activity among the class mollicutes

Uridine phosphorylase activity has been used to detect mycoplasmas in cell cultures by measuring formation of¹⁴C-uracil from¹⁴C-uridine. In this report we show that all species ofMycoplasma, Acholeplasma, andUreaplasma tested exhibited uridine phorphorylase activity. Among the genusSpiroplasma, serogroups I-1, I-3, I-5, I-7, I-8, IV, XIII, and XIV lacked uridine phosphorylase activity.Present address: Ciba-Geigy, Basel, Switzerland.     

Approximate case influence for the proportional hazards regression model with censored data

A method is presented for approximating the influence of individual cases upon regression coefficient estimates obtained from the Cox proportional hazards model. Observations can thus be identified which may greatly influence statistical inferences regarding the effects of prognostic factors upon survival time. An example from a cancer clinical trial is given.     

Two models for a maternal factor in the inheritance of Huntington disease

Huntington disease is a classic example of an autosomal dominant trait. Over the years, however, a number of investigators have reported anomalies regarding the age of onset of the disease that are inconsistent with this paradigm. We propose two models in which a maternal factor--cytoplasmic in one case, autosomal or X-linked in the other--acts to delay onset in a manner consistent with the previously reported anomalies. Relevant data from the Huntington's Disease Research Roster are presented that reinforce and extend the previous observations.     

Telomere conversion in trypanosomes.

Activation of the gene coding for variant surface glycoprotein (VSG) 118 in Trypanosoma brucei proceeds via a duplicative transposition to a telomeric expression site. The resulting active expression-linked extra copy (ELC) is usually flanked by DNA that lacks sites for most restriction enzymes and that is thought to interfere with the cloning of the ELC as recombinant DNA in Escherichia coli. We have circumvented this problem by cloning an aberrant 118 ELC gene, flanked at the 3'-side by at least 1 kb DNA, that contains restriction enzyme sites. Our analysis shows that this DNA and the 3'-end of the 118 ELC gene are derived from another VSG gene (1.1006) that is permanently located at a telomeric position. We propose that the 3'-end of the 1.1006 gene and (all of) its 3' flanking sequence moved to the expression site by a telomere conversion. Such a telomere conversion can also account for the appearance of an extra copy of the 1.1006 gene detected in a sub-population of our trypanosome strain.     

Regional differences in the distribution of golgi cells in the cerebellar cortex of man and some other mammals

Summary The number of Golgi cells per unit volume was determined in different regions of the cerebellar cortex of man and of ten other mammals. Despite the general belief in the uniform architecture of the cerebellar cortex, regional differences in the distribution of Golgi cells were found. In the inferior parts of the vermis, the number of Golgi cells per unit volume is twice that in the corresponding hemispheres. In addition, there are differences between the anterior and inferior parts of the vermis. These differences are a feature of the cytoarchitecture of the cerebellum in man and all the investigated mammals. The ratio of Purkinje cells to Golgi cells was also determined and found to differ in different species. In man, this ratio is 11.5, while in the monkey and cat it is almost 11.9 and in the rat 13.3. These differences in the ratio of Purkinje cells to Golgi cells are discussed from the point of view of cerebellar evolution.Supported by the Deutsche Forschungsgemeinschaft.     

Die Plastidenverteilung bei der Mitose der Schließzellenmutterzellen von haploidem Schwedenklee (Trifolium hybridum L.)

Summary In order to investigate whether during mitosis of guard cell mother cells the plastids are distributed to the daughter cells at random, a haploid of Trifolium hybridum, a species with only three to four chloroplasts in one diploid guard cell, was searched for and found. As expected, the guard cell mother cells in this plant contained only about two plastids. If distribution to the daughter cells would occur strictly at random, among the guard cell pairs with two chloroplasts the pairs with 1/1 and those with 2/0 chloroplasts should appear in equal amounts. However, 159 pairs of type 1/1 and only 35 pairs of type 2/0 were found, i.e., 18% of type 2/0 (upper limit of 99% confidence interval: 25%), indicating that the plastids have been apportioned to a fairly great degree. The result may be understood by considering that the plastids in guard cell mother cells are not scattered at random throughout the cell space, but are more regularly spread as are the chloroplasts in adult cells.