Sperm RNAs

An enzyme that uses an RNA template to add DNA to the ends of chromosomes. Telomerase is normally active only in stem cells and those cells giving rise to sperm and egg, but telomerase also undergoes activation when cells become cancerous. In the latter case, telomerase action allows transformed cells to replicate without a limit, a process termed immortalization . 

Pure salmon sperm DNA (41 % dG + dC), from Worthington Biochemical Co., Freehold, New Jersey, USA, was used. Protein content in it was determined by the method of Lowry et al. and found to be less than 1 %. RNA content, determined by Defrance and Delesdain s method was also less than 1 %. DNA absorption... 

Trichloroethane bound to DNA, RNA and protein in liver, lung, kidney and stomach of mice and rats given a single intraperitoneal injection but did not induce micronuclei in mouse bone marrow following two injections, or abnormal sperm morphology in mice given five daily intraperitoneal injections. 

Trichloroethane covalently bound to DNA, RNA and protein in mice and rats but did not induce micronuclei or abnormal sperm head morphology in mice in vivo. It induced chromosomal aberrations and cell transfonnation in mammalian cell cultures and it showed inconclusive evidence of sister chromatid exchange induction. It did not induce unscheduled DNA synthesis or gene mutation in mammalian cells in vitro. 

I The first and simplest of them are those of sperm-head nucjeo-protein [17]. Here the nucleic acid, DNA, seems to determine the structure. In the gap already mentioned between the coils of the double spiral there is no room for any more nucleotide, but only for the smaller protamine chain, as Wilkins has shown. No similar structure has been found for natural RNA but it does occur for the combination of two different artificial poly-adenosine ribose phosphate and guanine ribose phosphate. This fact, established by Rich [18], is the best example of heterogeneous mutual coiling in vitro of polymer molecules. 

The discovery of deoxyribonucleic acid dates to 1869, when Miescher isolated a new chemical substance from white blood cells that he obtained from pus and later from sperm cells.3 The material, which became known as nucleic acid, occurred in both plants and animals, thymus glands and yeast cells being among the best sources. Chemical studies indicated that the nucleic acids isolated from thymus glands and from yeast cells were different. As we now know, thymus nucleic acid was primarily DNA and yeast nucleic acid primarily RNA. For a while it was suspected that animals contained only DNA and plants only RNA, and it was not until the early 1940s that it was established that both substances were present in all organisms.3 ... 

Selenium plays a special role in development and protection of spermatozoa (Chapter 15). Tire selenoprotein phospholipid hydroperoxide glutathione peroxidase (PHGPx Eq. 15-58, Table 15-4) has a high activity in the testis and in spermatids. However, in mature spermatozoa it forms an enzymatically inactive oxidatively crosslinked capsular material around the midpiece of the cell perhaps providing mechanical stability.268 A similar 34-kDa selenoprotein is present in sperm nuclei and may be essential for condensation of DNA.269 Sperm tails contain specialized cytoskele-tal proteins which form "outer dense fibers."270 In contrast to mammalian spermatozoa, nematode sperm move by ameboid motility that depends upon a specialized actin-like molecule.271 Sperm cells are unusually rich in polyamines, most of which are bound to RNA and DNA (Chapter 24). 

Figures 15 and 16 show typical Py-El mass spectra of herring-sperm DNA and yeast RNA recorded on a Riber 1010 quadrupole mass spectrometer. The spectrum of the synthetic polynucleotide polydeoxyinosine-deoxycytosine (Fig. 17), recorded in a negative ion mode e capture), shows the essential characteristics of this polymer (jn/z 13 5 B for I and 110 B for C) as expected.

Since RNA double helices and most RNA/DNA hybrids have only been observed in conformations similar to the A-form [14-24] whereas studies of the DNA conformation in cells such as salmon sperm have revealed that the resting state of DNA appears to be the B-form [25], it is natural to speculate that the B-form is adopted for DNA replication whereas the A-form is adopted for transcription. Similar considerations apply in the case of synthetic polynucleotides a polynucleotide with a highly repetitive base sequence can be found in the S form under conditions in which a natural DNA with essentially random base sequence would be found in the B form. Highly repetitive sequences flanked on both sides by random sequences are known to exist in natural DNAs and so it is possible that under some ionic conditions the repetitive and random sequences would have different conformations. The potential to exploit such structural differences in control processes mediated by specific DNA-protein recognition mechanisms is clear. Although these speculations have not been confirmed, the fact that conformational transitions may be implicated in such fundamental biological processes is powerful justification for extensive study of the stereochemical pathways of these transitions and the factors which promote and control them. 

In 1868 Friederich Miescher isolated a substance from the nuclei of pus cells that he named nuclein. A similar substance was subsequently isolated from the heads of salmon sperm. Nuclein was later shown to be a mixture of a basic protein and a phosphorus-containing organic acid, now called nucleic acid. There are two forms of nucleic acids, DNA and RNA. 

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