Physiological Genetics (eBook)

John G. Scandalios (Herausgeber)

eBook Download: EPUB

2014 | 1. Auflage
292 Seiten
Elsevier Science (Verlag)
978-1-4832-7022-7 (ISBN)

Infos

Physiological Genetics is a compilation of developments, contributed by experts in the field of physiological genetics. The articles contained in the book covers various accounts of developments in the field. The book starts with an introductory chapter describing genetic factors in developmental gene regulation, followed by discussions on enzyme differentiation, hormonal control of gene expression, biochemical genetics of morphogenesis, cytoplasmic male sterility in maize, plant somatic cell genetics, and the population dynamics of genetic polymorphism. Physiologists, biologists, geneticists, and students will find a valuable reference material.

Textauszug

2

Control of Gene Expression and Enzyme Differentiation

JOHN G. SCANDALIOS

Publisher Summary

The catalase gene-enzyme system presents an attractive model for the study of post-translational regulation of differential gene expression in a complex eukaryote. This system is appropriate for studies on the genetic and epigenetic modulation of gene expression during development. The tissue specificity of catalase both qualitatively and quantitatively may be a reflection of the state of differentiation of a particular cell type or of its metabolic activity. The fact that the Cat1 and Cat2 mRNAs have been successfully isolated, partially purified, and proved to serve as active templates for the in vitro catalase synthesis in a cell-free system clearly renders this gene-enzyme system amenable to regulation studies at all possible levels.

I. Introduction

II. Isozymes

    

A. Definition

B. Molecular Bases of Isozyme Formation

C. Occurrence

III. The Enzyme Catalase: General Aspects

    

A. Some Characteristics

B. Occurrence

C. Genetic Variation

D. Biological Function and Intracellular Localization

IV. The Catalase Gene-Enzyme System of Maize: A Model System

    

A. Organism of Choice

B. Genetic Control of the CAT-1 Catalases

C. Developmental Control of Gene Expression

D. Regulation of Differential Cat1 and Cat2 Gene Expression

E. Purification of CAT-1 and CAT-2 mRNAs

F. Developmental Program Perturbations

G. Tissue-Specific Catalases (Spatial Programming)

H. The CAT-3 Isozyme of Young Leaves

I. Purification and Properties of Maize Catalases

J. Gene Effects on Catalase Structure and Function: A Case for Molecular Heterosis

V. Concluding Remarks

References

I INTRODUCTION

The programmed and precise expression of genes during development involves some of the most complex sequences of biochemical reactions observed in living cells. The molecular mechanisms by which information encoded in genes is decoded and translated into proteins are fairly well understood. However, the mechanism(s) whereby the cell controls or modulates the activity of its structural genes remains to be resolved. Although some of the mechanisms regulating gene expression have been resolved in prokaryotes, there is very little information on such mechanisms in the more complex eukaryotes. In fact, the data accumulated to date suggest that there are distinct and important differences in the controls identified in microbes and higher organisms.

The coordinated expression of genes observed during the development of complex eukaryotes is likely the result of the evolution of complicated regulatory mechanisms along with the increase and specialization of the genetic information as organisms evolved from the relatively simple to the more complex forms. There are, in fact, three general levels of control currently recognized: (a) “transcriptional control” (pertaining to the synthesis of messenger RNA), (b) “translational control” (pertaining to processing and utilization of messenger RNA), and (c) “posttranslational control” (pertaining to processing and modification of protein molecules following polypeptide synthesis). Each of these levels of control incorporates a number of precise points at which control can be exerted in regulating the expression of genes (Table I). Very little is currently known as to whether any one of the specific control points may be the most important in generating the ultimate phenotype. In the more complex eukaryotes these mechanisms, or control points, may operate at two basic levels of gene regulation during development and differentiation; these are (a) “spatial control” and (b) “temporal control.”

TABLE I

Some Possible Points of Control of Gene Expression

I.	Transcriptional control

1. Availability of the DNA template for transcription

2. Initiation of transcription (template recognition and binding of RNA polymerase to the template)

3. Rate of transcription (number and activity of RNA polymerase molecules)

4. Termination of transcription and release of mRNA

II.	Translational control

1. Processing and “maturation” of mRNA versus degradation (i.e., availability of mRNA for translation)

2. Transport of mRNA

3. Availability of mRNA and aminoacyl-tRNA synthetases

4. Availability of ribosome subunits

5. Formation of initiation complex

6. Initiation

7. Peptide bond formation and translocation

8. Termination of protein synthesis and release of protein

9. Continued availability of mRNA versus degradation

III.	Posttranslational control

1. Modification of protein structure (primary, secondary, tertiary, quaternary)

2. Activation or inactivation of protein

3. Synthesis versus degradation (rate of turnover)

4. Intracellular processing (compartmentation)

Analysis of enzyme expression provides a reasonable and promising approach toward understanding the regulation of gene expression in eukaryotes, providing we accept the underlying assumption that the characteristics of a given cell at different stages of development are functions of the protein (enzyme) molecules existing in those cells. Alternatively stated, since enzymes are necessary for the chemical reactions of living cells, the molecular bases for eukaryote development may be critically analyzed by studying the ontogeny of enzymes and the mechanisms regulating their expression and function in time (temporal) and in specific tissues (spatial). Since protein synthesis is a central process in the metabolism of the cell, it directly expresses the information encoded in the genes. However, biochemical development cannot only be described in terms of enzyme differentiation; nonenzymatic functional and structural proteins and other molecules play an integral part in the overall developmental profile of the organism. The uniqueness of enzymes is that they are all proteins and their behavior may reflect general principles underlying the developmental characteristics of nonenzymatic proteins as well, and the fact that, as a consequence of their catalytic properties, they may reflect the metabolic and differentiated state of cells. To a geneticist, enzymes serve as sensitive probes to monitor the developmental pattern of the encoding genes in an attempt to elucidate, at least at the posttranslational level, those control mechanisms that may underlie the differential expression of genes in the complex eukaryotes.

The important phenotypic characteristics of an enzyme are its properties as a catalyst, the regulation of its synthesis and degradation, and its distribution within cells and tissues. Since the catalytic properties of an enzyme are ultimately a consequence of its amino acid sequence, they can be altered by mutation of its structural gene. Such properties include catalytic efficiency, substrate specificity, physical stability, and response to regulatory effectors.

It is now a well known and accepted fact that enzymes can exist in multiple molecular forms, or “isozymes,” within the cells of a single organism. In fact, several hundred different enzymes are now known to exist in multiple molecular forms in a great variety of organisms. The subject has been discussed in detail elsewhere (Shaw, 1969; Scandalios, 1969, 1974; Eppenberger, 1975; Markert, 1968, 1977). This general phenomenon affords an opportunity for the study of the sequential development of organisms, that is, the isozymic profile of a cell reflects its state of differentiation, and, consequently, an understanding of the changing isozymic profile and the factors affecting it during development may...

Produkt-Details

• Erscheint lt. Verlag: 24.4.2014
• Sprache: englisch
• Themenwelt: Medizin / Pharmazie
• Themenwelt: Naturwissenschaften ► Biologie ► Evolution
• ISBN-10: 1-4832-7022-X / 148327022X
• ISBN-13: 978-1-4832-7022-7 / 9781483270227