Molecular basis of structure and function of the microvillus membrane of intestinal epithelial cells

Correlation of molecular structure with biochemical functions of the plasma membrane of the microvilli of intestinal epithelial cells has been investigated by biochemical and electron microscopic procedures. Repeating particles, measuring approximately 60 &#197;in diameter, were found on the surface of the microvilli membrane which had been isolated or purified from rabbit intestinal epithelial cells and negatively stained with phosphotungstic acid. These particles were proved to be inherent components of the microvillus membrane, attached to the outer surface of its trilaminar structure, and were designated as the elementary particles of the microvilli of intestinal epithelial cells. Biochemical and electron microscopic identification of these elementary particles has been carried out by isolation of the elementary particles with papain from the isolated microvillus membrane, followed by purification of the particles by chromatographies on DEAE-cellulose and Sephadex columns. The partially purified particles containing invertase and leucine aminopeptidase are similar in size and structure to those of the elementary particles in the microvillus membrane. Evidence indicates that each of the elementary particles coincide with or include an enzyme molecule such as disaccharidase or peptidase, which carry out the terminal hydrolytic digestion of carbohydrates and proteins, respectively, on the surface of the microvillus membrane. Magnesium ionactivated adenosine triphosphatase and alkaline phosphatase cannot be solubilized with papain but remains in the smooth-surface membrane after the elementary particles have been removed. Cytochemical electron microscopic observation revealed that the active site of magnesium ion-activated adenosine triphosphatase is localized predominantly in the inner surface of the trilaminar structure of the microvillus membrane.</p

Complete in vitro DNA replication of SV40 chromatin in digitonin-treated permeable cells.

A permeable cell system has been developed by treatment with digitonin for studying in vitro DNA replication of chromatin. DNA replication of simian virus 40 nucleoprotein complexes (SV40 chromatin) in digitonin-treated permeable cells was analyzed by electrophoresis in agarose-gel. Autoradiography of the agarose-gel revealed that [32P]dCTP was incorporated in SV40 DNA I, II and replicating intermediates. The time course of the incorporation indicated the complete replication of SV40 DNA and chromatin with a full number of nucleosomes. The digitonin-treated permeable cell system will serve as a useful system for studying in vitro DNA replication of chromatin.</p

A simple large-scale method for separating closed circular form DNA by gel electrophoresis

The covalently closed form of circular duplex SV40 DNA was separated from the open and linear form of SV40 DNA by agarose gel electrophoresis in a large-scale gel system. The closed circular DNA was recovered from agarose gels by re-electrophoresing the gel slices. The recovery of DNA was about 70%. Electron microscopic analysis showed that the recovered DNA did not have doube- or single-stranded breaks. The recovered DNA can be used without further purification for electron microscopy, as a substrate for experiments using restriction endonuclease and as a template for in vitro RNA synthesis.</p

Simian virus 40 chromatin showing nucleosomes in linear bead-like arrangements along extended closed circular DNA

Viral nucleoprotein complexes were extracted from nuclei of permissive cells (CV-1) infected with simian virus 40 (SV40) and examined by electron microscopy. SV40 nucleoprotein complexes (SV40 chromatin) showed nucleosomes in linear bead-like arrangements along the extended closed circular DNA. The contour length of the SV40 chromatin was only 1.0-1.8 times shorter than that of viral DNA obtained after deproteinization. The data suggest that the circular DNA in SV40 chromatin can be extended to nearly its full length without detachment of the histone complexes.</p

Type C virus particles produced in human T-cell lines derived from acute lymphoblastic leukemia and a leukemic T-lymphoid malignancy.

Electron microscopy of four human T-cell lines revealed the production of type C virus particles in two T-cell lines: one derived from acute lymphoblastic leukemia and the other from a leukemic T-lymphoid malignancy. Virus particles isolated from these cells had reverse transcriptase activity and the major internal structural protein of 30,000 daltons (p30). The indirect immunofluorescence test of these virus-producing cells with sera of patients with adult T-cell leukemia (ATL) was negative. The data indicate that these retroviruses are different from adult T-cell leukemia virus (ATLV).</p

Complete in vitro replication of SV40 DNA and chromatin in saponin-treated permeable cells.

A permeable cell system has been developed by treatment with saponin for studying in vitro replication of DNA and chromatin. DNA replication of simian virus 40 nucleoprotein complexes (SV40 chromatin) in saponin-treated permeable cells was found to be more efficient than that in digitonin-treated permeable cells. Autoradiography of the agarose-gel revealed that [alpha-32P]dCTP was incorporated into SV40 DNA I, II and replicating intermediates. The time course of the incorporation indicated complete replication of SV40 DNA and chromatin with a full number of nucleosomes. The saponin-treated permeable cell system will serve as a useful system for studying in vitro replication of DNA and chromatin in eukaryotic cells.</p

Rapid purification of squirrel monkey retrovirus-H major gag protein by high performance liquid chromatography.

The major gag protein (p34) of squirrel monkey retrovirus-H was purified in one chromatographic step by anion-exchange high performance liquid chromatography. The virus in a crude fraction was disrupted with Brij 35 in the presence of three kinds of protease inhibitors. The soluble virus lysate was injected into a Polyanion SI column, and p34 was eluted with a linear salt gradient. The recovery of the protein was about 60%. The purified p34 was nearly homogenous as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and silver staining.</p

Microinjection of nucleic acids into cultured mammalian cells by electrophoresis.

Simian virus 40 (SV40) DNA was microinjected into cultured mammalian cells by means of electrophoresis (iontophoresis). Successful transfer of DNA into cells was confirmed by detecting SV40 T antigen using the indirect immunofluorescent technique.</p

Non-radioactive hybridization probes prepared using M13 phage vector and the universal sequencing primer.

Non-radioactive hybridization probes were prepared using the M13 phage vector and the universal sequencing primer. The probe sequence to be used was first cloned into the M13 vector, and the minus strand of the template DNA was then synthesized with the Klenow fragment of E. coli DNA polymerase I in the presence of the biotinylated nucleotide, biotin-11-dUTP, as a label. Resultant DNA was heavily biotinylated, and made up of the entire minus strand of the template DNA. The long tag sequence derived from the M13 vector may increase the sensitivity of the detection. The biotinylated hybrids were visualized with the streptavidin-alkaline phosphatase conjugate and chromogenic substrates. As shown by Southern hybridization, the probe prepared in this way could be used to detect less than 1 pg of target sequence and a single copy gene sequence in human genomic DNA within several hours of signal development.</p

Partial purification of Simian virus 40 large T antigen by immunoaffinity chromatography and its detection by enzyme-linked immunosorbent assay.

Simian virus 40 (SV40) large T antigen was partially purified from small amounts of SV40-infected and SV40-transformed cells by immunoaffinity chromatography with high recovery. T antigen, in both crude and partially purified states, was detected rapidly by a sensitive and quantitative enzyme-linked immunosorbent assay (ELISA). Stability of the partially purified T antigen was found to increase by addition of 0.01% bovine serum albumin (BSA).</p