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B Calabretta

Publications and source records attributed to B Calabretta.

174 records · Page 10Linked to original sources
PubMed1985

Recent amplification of an alpha satellite DNA in humans.

A repeat sequence 682 base pairs (bp) long produced by cleavage of human DNA with Xba I restriction enzyme is composed of four tandemly arranged subunits with lengths of 171, 170, 171, and 170 bp each. The sequence organization of the 682 bp Xba I repeat bears a striking resemblance to other complex satellite DNAs of primates, including the Eco RI human alpha satellite family which also occurs as a 170 bp repeat. The Eco RI tetramer and the 682 bp Xba I repeat show a sequence divergence of 21%. The 682 bp Xba I repeat sequence is restricted to humans and is only distantly related to the previously reported 340 bp Xba human repeated DNA sequence. These finding are consistent with the concept of occasional amplifications of members or groups of members of alpha satellite DNA during human evolution. Amplifications apparently occurred after humans, apes and gibbons diverged from Old World monkeys (Eco RI satellite), after humans and apes diverged from gibbons (340 bp Xba I satellite) and after humans diverged from the great apes (682 bp Xba I satellite).

Animals↗
PubMed1985

Cell-cycle-specific genes differentially expressed in human leukemias.

Three cDNA clones isolated from Syrian hamster cells (p4F1, p2F1, and p2A9) contain sequences that are preferentially expressed in the G1 phase of the cell cycle. The expression of these sequences was investigated in human peripheral blood cells from normal individuals and from patients with leukemia. The expression of p4F1 and p2F1 is clearly dependent on the cell cycle in peripheral blood mononuclear cells stimulated to proliferate with phytohemagglutinin; the p2A9 sequences cannot be clearly detected in human lymphocytes but are expressed in a cell-cycle-dependent manner in human diploid fibroblasts (WI-38). These genes also show different levels of expression in lymphoid and myeloid leukemias. The highest level of expression for p2A9 is found in patients with chronic myelogenous leukemia, and the lowest in patients with chronic lymphocytic leukemia. For p2F1 and p4F1, the highest levels of expression are found in chronic and acute myelogenous leukemia. At least two other cell-cycle genes are not expressed at detectable levels in human leukemias. These findings suggest that the activation of cell-division-cycle genes might contribute, like cellular oncogenes, to the phenotype of human malignancies and that, perhaps, new oncogenes could be found by identifying and isolating genes whose expression is dependent on the cell cycle.

Cell Cycle↗
PubMed1985

Expression of cell-cycle-dependent genes in phytohemagglutinin-stimulated human lymphocytes.

We have investigated the expression of certain cell-cycle-dependent genes in human peripheral blood mononuclear cells (PBMC) stimulated by phytohemagglutinin (PHA). The genes studied had been previously identified as cell-cycle dependent in other cell types from different species and were induced by different mitogens. One of these genes (2F1) and the gene for the interleukin 2 receptor were induced by PHA even in cultures partially depleted of accessory cells where the lymphocytes grew in size but failed to enter S phase. The other genes (c-myc, 4F1, JE-3, and KC-1) were induced only in complete cultures of PBMC stimulated by PHA. These results confirm the dissociation between growth in size and cell DNA replication that can occur during cell-cycle progression. Moreover, the time course of appearance of detectable levels of RNA for these genes suggests that they may be used as markers of cell-cycle progression in the transition of lymphocytes from G0 to S phase.

Cell Cycle↗
PubMed1985

Expression of c-myc and other cell cycle-dependent genes in human colon neoplasia.

We have investigated the expression of certain cell cycle-dependent genes in total RNA isolated from normal and neoplastic cells of human epithelial colon tissue. The genes studied had been previously identified as cell cycle dependent in rodent and human fibroblasts. Levels of expression of G1 genes were compared to the level of expression of the S-phase-specific gene H3 in normal and adjacent neoplastic epithelial cells of six different individuals. We have found that the increase in the expression of c-myc gene detected in colon tumor cells is accompanied by a parallel increase in the expression of two G1-specific genes (p2A9 and ornithine decarboxylase) and the S-phase-specific gene histone H3. An important conclusion that can be drawn from these findings is that the increased level of a cell cycle-specific RNA in a tumor may not indicate overexpression of that gene but simply reflect the increased fraction of cycling cells, unless the ratio of expression between G1 genes and G1-S-phase genes is altered.

Adenocarcinoma↗
PubMed1981

mRNA in human cells contains sequences complementary to the Alu family of repeated DNA.

Approximately one-half of the polysomal poly(A)+RNA from CCRF-CEM human lymphoblastoid cells associates at low R0t (10 M.sec) [where R0 is the initial concentration of RNA (M) and t is time (sec)] to form branched complexes detectable by electron microscopy. The complexes typically involve 2-16 molecules associated over double-stranded regions 120 +/- 30 base pairs long. Formation of such complexes suggests that poly(A)+RNA contains repeated-sequence elements that are highly represented in the mRNA population. Hybridization of polysomal poly(A)+RNA with a recombinant human DNA plasmid, p lambda H15C, which is shown to contain at least three regions complementary to two different members of the Alu family of DNA repeat sequences, showed a total of five regions where R loops are formed. The hybridized regions comprising these groups are 260 +/- 180, 240 +/- 170, 150 +/- 70, 180 +/- 60, and 180 +/- 80 base pairs long. The relative frequencies of R loops formed at these different sites indicate that sequences in this recombinant DNA are represented in the mRNA population at different frequencies. The hybridizing sequence of the RNA molecules is located near one terminus in 13% of the R loops and internally in 53% of the R loops. Surprisingly, 35% of the R loops apparently involve RNA molecules hybridized over their entire length of only 200 +/- 110 base pairs.

Cell Line↗
PubMed1981

Presence of a highly repetitive and widely dispersed DNA sequence in the human genome.

A genomic DNA library consisting of human DNA fragments about 18 kilobases long cloned in a bacteriophage lambda vector was found to contain a specific repeated DNA segment. The repeated sequence is present in greater than 95% of the genomic library, and selected clones contain at least two copies of the sequence. Our experiments indicate that this highly repetitive sequence (approximately 400,000 copies per haploid genome) is widely distributed in the human genome and is represented in the cytoplasmic polysomal mRNA. This sequence is homologous to the 300-base-pair Alu repeat family, the predominant repeat sequence in man.

Cloning, Molecular↗
PubMed1979

Kinetics of hybridization to human DNA of heterogeneous nuclear RNA isolated from normal human lymphoblasts and acute leukemia blast cells.

Heterogeneous nuclear RNA was extracted from normal PHA-stimulated human lymphocytes and acute myeloid leukemia blast cells. Experiments were performed to determine the hybridization kinetics of these RNA's to human DNA. The best least squares solutions indicate in the hybridization reaction of both normal and leukemic RNA two main components. For leukemic cell RNA the rate constants of both components were significantly different from that of normal cell RNA. In particular, the difference between the rate constants of the second lower component suggests that the slowly hybridizing sequences in leukemic cell RNA have a degree of repetition higher than of the corresponding sequences of normal cell RNA.

Base Sequence↗