ABSTRACTS:

ARTICLE TITLE: PUFFS AND PCR: THE IN VIVO DYNAMICS OF EARLY GENE EXPRESSION DURING
ECDYSONE RESPONSES IN DROSOPHILA
AUTHORS: F. HUET, C.RUIZ AND G.RICHARDS
JOURNAL: DEVELOPMENT, 1993 Jun;118(2):613-27
Abstract: A hormone in Drosophila (the fruit fly) orchestrates insect development by regulating gene networks. This is seen in the sequential activation of early and late puffs in the chromosomes of the late larval salivary gland. (The salivary gland chromosomes are large and easily seen under a microscope.) These chromosome puffs and the hormonal effects probably occur at both at the transcriptional (induced puff) and translational (induced protein) levels. The naturally occurring puffs seem to have heat induced counterparts. Whenever the flies are subjected to an elevated temperature, the heat stress augments or creates larger puffs. One puff present under control (25 degrees C) conditions was found to increase in size in response to stress in all species. A number of these early puffs contain complex transcription encoding families of regulatory proteins which are expressed in most if not all tissues. Thus the study of these elements in the fruit fly may have applications to many other specie.

Associated with the production of heat induced chromosomal puffs are large heat shock particles. These may represent dormant or newly synthesized heat shock RNA associated with proteins. Three distinct hormone responses have been characterized. The relatively brief prepupal response contains elements in common with each of the larval responses and all three can be explained by the profiles of the respective hormone peaks. Interestingly some transcripts respond differently during each response. Analysis of different tissues of the same animal reveals subtle differences in the timing of the hormone response and isoform expression and suggests that this may reflect tissue differences in the hormone profiles. As these molecules have homologues in vertebrates, our analysis may have general implications for the organization of hormonal responses in vivo.

KEY WORDS/PHRASES
GENE NETWORKS
HEAT SHOCK PARTICLES
HEAT SHOCK RNA
HOMOLOGUES
HORMONE
INSECT DEVELOPMENT
REGULATORY PROTEINS
PUFFS
SEQUENTIAL ACTIVATION

TITLE: THE HUMAN IMMUNODEFICIENCY VIRUS TYPE 1 5' PACKAGING SIGNAL STRUCTURE AFFECTS TRANSLATION BUT DOES NOT FUNCTION AS AN INTERNAL RIBOSOME ENTRY SITE STRUCTURE.
AUTHORS: G.MIELE, A.MOULAND, G.P.HARRISON, E.COHEN, A.M.LEVER
JOURNAL: JOURNAL OF VIROLOGY 1996 Feb;70(2):944-51
Abstract: The role of the RNA secondary structure in the 5' packaging signal region of human immunodeficiency virus type 1 (HIV-1) in disrupting normal translation of mRNA has been investigated both in vitro and in the presence of cellular cofactors in vivo. Destruction of this structure leads to an increase in levels of translated products, indicating that the structure is a significant inhibitor of translation (that is, it normally blocks translation.)
The closeness of several ribosome entry ports to the packaging signal structure suggested that it might function as an internal ribosome entry site. If a strand of mRNA happened to enter through third port instead of its normal port on the ribosome, abnormal proteins would be manufactured. In the case of HIV-1 these abnormal proteins interfere with normal T-cell function. The packaging signal structure causes significant translational inhibition. Perhaps a single amino acid substitution in one of the ribosome subunits disrupts interaction between the ternary complex and the ribosome. Other factors to consider include the ribosome recycling factor (ribosome releasing factor) which is essential for bacterial growth. Ribosome releasing factor is responsible for dissociation of ribosomes from mRNA after the termination of translation. Since it functions to "recycle" ribosomes, it is also called ribosome recycling factor.
Another aspect of translation to consider may be mutational enhancement. Specialized ribosomes carry a mutation in the region of 16 S rRNA, which is the site of mRNA binding. A complementary mutation in the ribosome binding site of a particular mRNA results in specific and efficient translation of this mRNA on the specialized ribosomes. Translation of specialized mRNA on specialized ribosomes gave 5 times more enzyme activity than did translation of wild-type mRNA on wild-type ribosomes under similar conditions. Ribosomal protein S15 from Escherichia coli modulates its own translation by trapping the ribosome on the mRNA initiation loading site.

KEY WORDS/PHRASES
CELLULAR COFACTORS
ENZYME ACTIVITY
mRNA INITIATION LOADING SITE
MUTATIONAL ENHANCEMENT
RIBOSOME RECYCLING FACTOR
TRANSLATION
TRANSLATIONAL INHIBITION

TITLE: MOLECULAR EVOLUTION OF TRANSFER RNA FROM TWO PRECURSOR HAIRPINS: IMPLICATIONS FOR THE ORIGIN OF PROTEIN SYNTHESIS.
AUTHORS: DICK T.P. AND W.A.SCHAMEL
JOURNAL: JOURNAL OF MOLECULAR EVOLUTION 1995 Jul;41(1):1-9
Abstract: This paper presents a model for the coevolution of major components of the protein synthesis machinery in a primordial RNA world. It proposes that the essential prerequisites for RNA-based protein synthesis, i.e., tRNA-like molecules, ribozymic charging catalysts, small-subunit(SSU) rRNA, and large-subunit(LSU) rRNA, evolved from the same ancestral RNA molecule. Several arguments are considered which suggest that tRNA-like molecules were derived by tandem joining of template-flanking hairpin structures involved in replication control. It is further argued that the ancestors of contemporary group I tRNA introns catalyzed such hairpin joining reactions, themselves also giving rise to the ribosomal RNAs.

One model includes a general stereochemical principle for the interaction between ribozymes and hairpin-derived recognition structures, which can be applied to such seemingly different processes as RNA polymerization, tRNA decoding, and peptidyl transfer, implicating a common origin for these fundamental functions. Others have demonstrated that certain proteins can promote formation of joint molecules when the duplex contains an RNA/DNA hairpin and a single-stranded circle serves as the pairing partner. A chimeric RNA/DNA hairpin can be used to form stable joint molecules with as little as 15 bases of shared homology as long as the RNA stretch contains complementarity to the circle. The joint molecule bears some resemblance to a triple helical structure composed of RNA residues surrounded by two DNA strands which are in a parallel orientation. These and other considerations suggest that generation and evolution of tRNA were coupled to the evolution of synthetases, ribosomal RNAs, and introns from the beginning and have been a consequence arising from the original function of tRNA precursor hairpins as replication and recombination control elements.

KEY WORDS/PHRASES
ANCESTRAL RNA
CHIMERIC
COEVOLUTION
HAIRPIN-DERIVED RECOGNITION STRUCTURES
HOMOLOGY
INTRONS
PROTEIN SYNTHESIS
RIBOZYMIC CHARGING CATALYSTS
RIBOSOMAL RNAS
tRNA
STEREOCHEMICAL PRINCIPLE