At high concentrations, free radicals and radical-derived, nonradical reactive species are hazardous for living organisms and damage all major cellular constituents. At moderate concentrations, how...

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Free Radicals in the Physiological Control of Cell Function

Analyses of steroid receptors are important for understanding molecular details of transcriptional control, as well as providing insight as to how an individual transacting factor contributes to cell identity and function. These studies have led to the identification of a superfamily of regulatory proteins that include receptors for thyroid hormone and the vertebrate morphogen retinoic acid. Although animals employ complex and often distinct ways to control their physiology and development, the discovery of receptor-related molecules in a wide range of species suggests that mechanisms underlying morphogenesis and homeostasis may be more ubiquitous than previously expected.

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The steroid and thyroid hormone receptor superfamily

Chromatin is not an inert structure, but rather an instructive DNA scaffold that can respond to external cues to regulate the many uses of DNA. A principle component of chromatin that plays a key role in this regulation is the modification of histones. There is an ever-growing list of these modifications and the complexity of their action is only just beginning to be understood. However, it is clear that histone modifications play fundamental roles in most biological processes that are involved in the manipulation and expression of DNA. Here, we describe the known histone modifications, define where they are found genomically and discuss some of their functional consequences, concentrating mostly on transcription where the majority of characterisation has taken place.

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Regulation of chromatin by histone modifications

The role of Jun, Fos and the AP-1 complex in cell-proliferation and transformation.

The small (40S) subunit of eukaryotic ribosomes is believed to bind initially at the capped 5'-end of messenger RNA and then migrate, stopping at the first AUG codon in a favorable context for initiating translation. The first-AUG rule is not absolute, but there are rules for breaking the rule. Some anomalous observations that seemed to contradict the scanning mechanism now appear to be artifacts. A few genuine anomalies remain unexplained.

/pdf/the-scanning-model-for-translation-an-update-52r2in8l71.pdf

The scanning model for translation: an update.

RETINOIC acid is a vitamin A derivative with striking effects on development and cell differentiation1–3. Several nuclear retinoic acid receptors (RARs), acting as ligand-inducible transcription factors, have been characterized4–8 and indirect evidence suggests that they have distinct roles9–11. One of the most intriguing properties of retinoic acid is its ability to induce in vivo differentiation of acute promyelocytic leukaemia (APL) cells into mature granulocytes, leading to morphological complete remissions12–13. Because the RARα gene maps to chromosome 17q21 (ref. 14), close to the t(15;17) (q21–qll–22) translocation specifically associated with APL15, we analysed RARα gene structure and expression in APL cells. We report here that, in one APL-derived cell line, the RARα gene has been translocated to a locus, myl, on chromosome 15, resulting in the synthesis of a myl/RARα fusion messenger RNA. Using two probes located on either side of the cloned breakpoint, we have found genomic rearrangements of one or other locus in six patients out of eight, demonstrating that the RARα and/or myl genes are frequently rearranged in APL and the breakpoints are clustered. These findings strongly implicate retinoic acid receptor α in leukaemogenesis.

The t(15;17) translocation of acute promyelocytic leukaemia fuses the retinoic acid receptor α gene to a novel transcribed locus

The PML-RARα fusion mRNA generated by the t(15;17) translocation in acute promyelocytic leukemia encodes a functionally altered RAR

DNA recombinant technology has radically changed hepatitis B virus (HBV) virology. The genetic organization, transcription and replication of the virus are basically understood, structures of integrated HBV sequences in hepatocellular carcinoma have been characterized, and new vaccines produced by recombinant DNA technique are being developed.

The hepatitis B virus

Retinoic acid, the first morphogen described so far in vertebrates, is a vitamin A derivative which exerts striking effects on development and differentiation. The identification of three retinoic acid receptors as members of the nuclear receptor super-family provides an explantation for the molecular action of morphogens on gene expression. Functional analysis of the receptors requires the identification of target genes and of their cis-acting retinoic acid-responsive elements. We have previously shown that the retinoic acid receptor beta gene is transcriptionally up-regulated by retinoic acid and now report the characterization of a functional retinoic acid responsive element in the beta gene that mediates trans-activation by retinoic acid. Using deletion mapping, we have identified a 27-base pair fragment, located 59 base pairs upstream of the transcriptional start, which confers retinoic acid responsiveness on the herpes virus thymidine kinase promoter. This sequence contains a perfect direct repeat of the motif GTTCAC, which is reminiscent of the 5' half-palindrome of the thyroid and oestrogen hormone responsive elements. Specific binding of the beta protein to the retinoic acid responsive element is demonstrated and is independent of the presence of retinoic acid. Both alpha and beta receptors enhance retinoic acid response in CV1 cells, indicating that they can both act through the same DNA sequence.

Anne Dejean

Papers

The t(15;17) translocation of acute promyelocytic leukaemia fuses the retinoic acid receptor α gene to a novel transcribed locus

The PML-RARα fusion mRNA generated by the t(15;17) translocation in acute promyelocytic leukemia encodes a functionally altered RAR

The hepatitis B virus

Identification of a retinoic acid responsive element in the retinoic acid receptor & beta;gene

The nucleoporin RanBP2 has SUMO1 E3 ligase activity