Role In Elongation Research Articles

Immunohistochemical Study on Localization of Tenascin in the Cervical Region of Rat Spinal Cord During Development.

Tenascin (TN) is transiently expressed in some organs and tumors at various developmental stages. It has also been reported that tenascin was a major extracellular matrix component in a developing nervous system, and played an important role in neurite outgrowth and pattern formation of the cerebral and cerebellar cortices.In the present study, we examined, under light and electron microscopes, the localization of TN in the cervical region of rat spinal cord during the late prenatal and early postnatal stages by means of conventional and immunohistochemical methods. In the specimens stained with hematoxylin-eosin and thionin, the following results were obtained: the structure of spinal cord was developing at the postnatal stages and attained a definite form around the 5th day after birth. Nissl bodies in neurons were maturing during this period and the processes of neurons elongated toward white matter. Concomitantly, neuroglia were also increased in the white matter.In accordance with it, luxol fast blue (LFB) and sudan black B stainable substances appeared in the white matter, especially ventral and lateral funiculi around the 5th day of age.The results of immuno-light microscopical observation showed that TN-labeling was observed only in the gray matter of the spinal cord at the 18th day of gestation, but both in gray and white matters from the 20th day of gestation to the 5th day after birth. The most intense TN-labeling was detected in the boundary of gray and white matter in the ventral and lateral funicili at the 2nd to 5th day after birth. As the development proceeded, up to the 2nd week after birth, TN-labeling was mainly distributed in the white matter except for the ventral region of dorsal funiculus and almost completely disappeared from the gray matter. Here, it was also noticed that the ventral region of dorsal funiculus became stainable with LFB or sudan black B between the 2nd and 3rd week after birth and at the same stage of development, TN-labeling became detectable in this region.At the electron microscopical level, TN-labeling was detected in the intercellular spaces of the gray matter during the 1st to 10th day of age. That is, TN was expressed associating with the cytoplasmic membrane and processes of neurons and neuroglia. TN-labeling was also observed along the cytoplasmic membrane of myelinating oligodendrocytes and in the cytoplasm of neuroglia, especially oligodendrocytes in the white matter at the 10th day to the 2nd week after birth. Clear reaction products for TN could not be detected in the synaptic region.From this evidence, it is concluded that TN mediates the interaction of neuron and neuroglia during late prenatal and early postanatal stages and plays an important role in elongation of neuronal processes and migration of neuroglia as well as the myelination in the developing rat spinal cord.

Requirement for the replication protein SSB in human DMA excision repair

Replication and repair are essential processes that maintain the continuity of the genetic material. Dissection of simian virus 40 (SV40) DNA replication has resulted in the identification of many eukaryotic replication proteins, but the biochemistry of the multienzyme process of DNA excision repair is less well defined. One protein that is absolutely required for semiconservative replication of SV40 DNA in vitro is human single-stranded DNA-binding protein (SSB, also called RF-A and RP-A). SSB consists of three polypeptides of relative molecular mass 70,000, 34,000 and 13,000, and acts with T antigen and topoisomerases to unwind DNA, allowing the access of other replication proteins. Human SSB can also stimulate the activity of polymerases alpha and delta, suggesting a further role in elongation during DNA replication. We have now found a role for human SSB in DNA excision repair using a cell-free system that can carry out nucleotide excision repair in vitro. Monoclonal antibodies against human SSB caused extensive inhibition of DNA repair in plasmid molecules damaged by ultraviolet light or acetylaminofluorene. Addition of purified SSB reversed this inhibition and further stimulated repair synthesis by increasing the number of repair events. These results show that a mammalian DNA replication protein is also essential for repair.

The role of gene O protein in the replication of bacteriophage λ

The role of the product of gene O of bacteriophage λ in phage DNA replication was examined by shifting cells infected with an Ots mutant to the nonpermissive temperature after incubation at the permissive temperature. Thymidine incorporation after the temperature shift exhibits biphasic kinetics, with rapid synthesis immediately after the shoft and slower synthesis 2–15 min after the shift. Following a shift to the nonpermissive temperature early in infection, the proportion of replicative intermediates decreases substantially and σ-structures are favored for preservation. When the shift is done late in infection, the proportion of replicative intermediates remains the same. The average length of single-stranded regions at the branch points increases after a shift to the nonpermissive temperature. Most of the counts which are incorporated after the temperature shift are incorporated into strands which are longer than unit length. These results favor a model in which λ O protein is required for the initiation of replication, but at least some elongation can continue in the absence of O. It is possible that O protein plays a role in elongation of the lagging strand at replicative forks. This model suggests a way to regulate the transition between θ and σ replication which occurs as λ infection proceeds.

In vitro replicative arrest in dnaAts mutants

Toluene-treated Escherichia coli, conditionally defective in initiation of DNA replication, have been studied. Toluenized mutants of the dnaA ts, class rapidly stop DNA synthesis at the restrictive temperature. This is in contrast to the slow arrest of replicative synthesis noted in vivo in these strains. The in vitro cessation of replicative DNA synthesis can be prevented by the presence of the detergent Triton X-100. Our results suggest a role in elongation of DNA by the dnaA gene product during replicative synthesis in vitro.