Quantitation of ovalbumin mRNA in hen and chick oviduct by hybridization to complementary DNA. Accumulation of specific mRNA in response to estradiol

Rapid regulation of c-myc protooncogene expression by progesterone in the avian oviduct

The mRNA levels of genes known to be regulated by sex steroids are not altered until 1 hr or longer after steroid treatment, although the steroid receptor complexes are bound to nuclear acceptor sites within 5 min. In a search for early regulation of gene transcription, total chick oviduct RNA was isolated at various times after injection (i.p.) of progesterone and analyzed for c-myc expression. Levels of c-myc mRNA began to decrease in response to progesterone by 10 min after injection. The mRNA levels continued to decrease, reached a 70% reduction at 30 min, and returned to control values by 8 hr after steroid injection. Changes in alpha-tubulin mRNA levels were markedly less in these same RNA preparations. The effect was dependent on the dose of the steroid and was target-tissue specific. These changes occurred much more rapidly than changes in egg-white protein mRNA levels. Vehicle alone did not alter c-myc mRNA levels. Early regulated genes such as c-myc may represent the initial site of action of steroid receptors in the genome.

Analysis of the membrane-associated poly(A)+RNA in the cytoplasm of dormant Artemia cysts by DNA excess hybridization. Evidence for a nuclear origin

Encysted embryos of Artemia contain latent mRNA, to a large extent associated with a fraction of cytoplasmic membranes. The membranes, purified by EDTA treatment and banding in a sucrose gradient at 1.17 g/cm3, include endoplasmic vesicles and mitochondria. The origin of the membrane-associated poly(A)+RNA was therefore investigated. In gel electrophoresis poly(A)+RNA from the purified membranes of dormant cysts forms two distinct bands at approx. 3 . 10(5) and 5 . 10(5) Da. Later during development the lighter component decreases. Nuclei from dormant cysts are devoid of poly(A)+RNA, while nuclei from developing embryos (50% emergence) contain a predominant poly(A)+RNA component of approx. 5 . 10(5) Da. 125I-labelled preparations of nuclear DNA and of nuclear and membrane-associated poly(A)+RNA were used in reassociation and hybridization experiments with excess nuclear DNA. Poly(A)+RNA from the membranes of dormant cysts hybridized to nuclear DNA to the same extent as the nuclear poly(A)+RNA from developing embryos. The hybridization of labelled, nuclear poly(A)+RNA to nuclear DNA was strongly inhibited by unlabelled membrane RNA from either dormant cysts or developing embryos. It is concluded that the stored, membrane-associated poly(A)+RNA in dormant cysts is essentially of nuclear origin. The 5 . 10(5)-Da component is largely homologous with the corresponding component of nuclear poly(A)+RNA at later stages.

The ovalbumin gene is associated with the nuclear matrix of chicken oviduct cells

The DNA in a eucaryotic nucleus is arranged into a series of supercoiled loops that are anchored at their bases to the nuclear matrix. Using nuclease digestion, one can progressively cleave DNA from the loops, thereby isolating residual DNA that is progressively closer to the nuclear matrix anchorage sites. We have determined that the ovalbumin gene is preferentially associated with the nuclear matrix of chicken oviduct cells, but is not preferentially associated with the nuclear matrix of chicken liver cells. As a control, the beta-globin gene, which is not transcribed in oviduct cells, was found not to be preferentially associated with the oviduct nuclear matrix. The observation that the transcriptionally active ovalbumin gene is preferentially associated with the nuclear matrix may have significant implications for gene expression and the organization of nuclear DNA into supercoiled-loop domains.

The regulation of protein synthesis in heart muscle under normal conditions and in the adriamycin-cardiomyopathy

The regulation of cardiac protein synthesis, in particular messenger-RNA (mRNA) and polyribosome metabolism, has been investigated in normal rat heart muscle and in the adriamycin-cardiomyopathy by using newly developed methods for the isolation, characterization and in-vitro translation of cardiac polyribosomes and mRNA. The obtained data allow the following conclusions: 1. Normal heart muscle has a high content of polyribosomes (865 micrograms/g) and of mRNA (20-60 micrograms/g), and thus a high rate of protein synthesis. 2. The level of cardiac polyribosomes and mRNA is strictly age-dependent and much higher in young animals (2-3 x). This corresponds to a higher cardiac protein synthesis rate in young animals with a growing heart muscle, and shows that the protein-synthetic reserves of heart muscle decrease sharply with age. 3. Withdrawal of food for 1-3 days results in a pronounced decrease (-50% to -70%) of cardiac polyribosomes and mRNA, demonstrating that the cardiac protein synthesis reacts very sensitively to conditions of starving. 4. The cardiac polyribosomes and mRNA are unevenly distributed in the myocyte. The bulk of these substances is present in the cardiac microsomes, and much less is found in nuclei, myofibrils, mitochondria and in the post-microsomal fraction (=cell-sap) of the cardiac muscle. This shows that the major intracellular site of cardiac protein synthesis is the microsomal fraction of the myocyte. 5. A pool of untranslated mRNA was demonstrated to be present in the cell-sap of the myocyte. This mRNA is to some extent translatable in-vitro and appears to represent mRNA sub-pools with two functions: a) mRNA which is partially broken down or in the process of being broken down, and b) intact mRNA which could have a "reserve-function", e.g., by being utilized to increase cardiac protein synthesis under certain conditions. 6. A method of quantitating small amounts of cardiac mRNA (25-50 ng) has been developed which makes it possible to estimate the mRNA content of cardiac biopsies. 7. These methods were utilized to study the relevance of changes in RNA- and protein synthesis in the development of the adriamycin-cardiomyopathy. It appears that severe decreases in cardiac mRNA and polyribosome levels are a key factor in the pathogenesis of the adriamycin-cardiomyopathy. These decreases are probably caused by the direct binding of adriamycin to cardiac DNA and lead themselves to a persisting decrease in cardiac protein synthesis which in view of the short half-lives of the cardiac contractile proteins (5-12 days) causes a gradual loss of cardiac structure and function.

DNA organisation in the chicken lysozyme gene region

DNA sequences surrounding the lysozyme gene of the chicken have been cloned in several recombinants which define a region of 40 Kb. We have detected no other gene with a sequence related to that of the lysozyme gene, nor any gene expressed in the oviduct in these recombinants. This situation contrasts with that of the ovalbumin gene, in the vicinity of which lie two other genes of related structure expressed in the oviduct under hormonal control. The lysozyme gene region, however contains a complex array of repeated sequences, which have been resolved into at least five classes. An inverted repeat overlaps the lysozyme gene itself.

Interaction of the chick oviduct progesterone receptor with deoxyribonucleic acid

The purified DNA binding component (receptor A) of the chick oviduct progesterone receptor has been analyzed for its ability to bind to the cloned ovalbumin gene and to plasmid DNA of various structural compositions. The rapid equilibrium filter adsorption assay of Riggs et al. [Riggs, A. D., Suzuki, H., & Bourgeois, S. (1970) J. Mol. Biol. 48, 67] has been used to demonstrate high affinity binding of the protein to DNA (Kdiss = 10(-10) M at 50 mM KCl, pH 7.2). Studies of association rates are consistent with equilibrium measurements (t 1/2 = 40-80 min). Association of purified receptor with DNA and the kinetics of the interaction have been verified independently by velocity sedimentation techniques. Direct binding assays were performed with the ovalbumin structural gene (cDNA), the entire natural ovalbumin gene containing seven intervening sequences, and various ovalbumin gene fragments coding for the 5' end of the nuclear precursor RNA, intron-exon junctions, and the 3'-noncoding region of the gene. No DNA-sequence specificity was identified for the binding of the receptor protein to any region of ovalbumin gene DNA. In contrast, the structural integrity of the DNA template greatly affected receptor binding. The poorest affinity was to supercoiled DNA and to blunt end, linear duplex gene fragments. The receptor bound saturably to DNA containing limited nicks but became nonsaturable as nicks were increased. Binding of the protein to double-stranded DNA increased susceptibility of the DNA to digestion by the enzyme S1, a single strand specific nuclease. On the basis of preferential receptor binding to single-stranded DNA, a possible mechanism involving DNA helix destabilization is discussed.

Commitment of chick oviduct tubular gland cells to produce ovalbumin mRNA during hormonal withdrawal and restimulation

Acute withdrawal of estrogen from chicks leads to a precipitous decline in egg white protein synthesis and egg white mRNAs in the oviduct. In this paper we explore the biochemical basis of this phenomenon as well as the capacity of the "withdrawn" tubular gland cells to be restimulated with steroid hormones. During withdrawal, the decline in ovalbumin mRNA was closely correlated with the decline in nuclear estrogen receptors. Within 2-3 d of estrogen removal a withdrawn state was established and then maintained, as defined by a 1,000-fold-lower level of ovalbumin mRNA and a 20-fold-lower level of nuclear estrogen receptors, relative to the estrogen-stimulated state. The number of active forms I and II RNA polymerases declined by 50% during this time. Histological examination of oviduct sections and cell suspensions, combined with measurements of DNA content, revealed that tubular gland cells persisted as a constant proportion of the cell population for 3 d after estrogen removal. Despite a 1,000-fold decrease in the content of ovalbumin mRNA, the ovalbumin gene remained preferentially sensitive to digestion by DNase I. When 3-d-withdrawn oviducts were restimulated with either estrogen or progesterone, in situ hybridization revealed that greater than or equal to 98% of the tubular gland cells contained ovalbumin mRNA. Induction by a suboptimal concentration of estrogen was correlated with a lower concentration of ovalbumin mRNA in all cells rather than fewer responsive cells.

Androgenic regulation of messenger RNA sequence complexity in accessory sexual tissues of the male rat studied with fractionated complementary DNA

Effects of androgens on mRNA sequence complexity in the rat seminal vesicle have been investigated using complementary DNA fractionated on the basis of sequence abundance. Total cDNA complementary to poly(A)-rich RNA from normal rats was hybridised with an excess of the same RNA to controlled rot values and then the free cDNA was separated from cDNA . RNA hybrids by hydroxyapatite chromatography. Three cDNA fractions were obtained with very different hybridisation characteristics. Abundant cDNA hybridised to an excess of its parental RNA with an rot 1/2 of 2.46 x 10(-3) mol 1(-1) s and is complementary to about six or seven average-sized sequences. Use of hybrid-arrested translation in a cell-free protein-synthesising system has shown that this class of mRNA includes mRNAs coding for major androgen-dependent secretory proteins. Moderate and scarce cDNA fractions each showed more complex hybridization kinetics; computer analysis suggested each is complementary to two groups of average-sized sequences. Each cDNA fraction was hybridised to excess poly(A)-rich RNA from normal or castrated rats and the kinetics compared. Castration had no effect on the total number of sequences present in any class and did not alter the relative concentration of the scarce sequences. A small (threefold) decrease was seen in the concentration of abundant sequences with a larger (tenfold) decrease in the moderate class. Both de-reases were reversed by testosterone in vivo. The results are consistent with earlier studies where the effects of testosterone on seminal vesicle mRNA were followed using a translation assay and confirm that no gross differential effects are exerted on abundant mRNA coding for major secretory proteins. The cDNA fractions were also used to investigate the overlap in genetic expression between seminal vesicle and ventral prostate. Both tissues share all the scarce sequences in the same relative abundance. Less than 0.0015% and 0.004% of prostatic mRNA is complementary to seminal vesicle abundant and moderate sequences respectively. Similarly prostatic abundant sequences account for less than 0.004% of seminal vesicle mRNA.

Distribution of RNA transcripts from structural and intervening sequences of the ovalbumin gene

A study was made of the function of the intervening sequences in the ovalbumin gene, Radioactively labeled DNA probes for the intervening sequences were prepared and RNA's were isolated from whole cells, nuclei, and polysomes of estrogen-stimulated chick oviducts. The concentrations of messenger RNA (mRNA) transcripts from ovalbumin structural sequences (mRNAov) and transcripts corresponding to intervening sequences were then estimated by hybridization to cloned DNA probes. Oviduct tissue contains approximately 58,000 molecules of mRNAov sequences per tubular gland cell and most of these sequences are present in the cytoplasm. In contrast, there are 200 to 300 molecules of RNA per cell which are transcribed from the intervening sequences of the natural ovalbumin gene and almost all of these are found in the nucleus. The difference in distribution of structural and intervening sequence transcripts suggests that, unlike mature mRNA, the intervening sequences are not preferentially transported to cytoplasmic polysomes.

Identification of potential ovomucoid mRNA precursors in chick oviduct nuclei

Denaturing gel electrophoresis of chick oviduct nuclear RNA reveals multiple species of RNA that are 1.5-5 times larger than ovomucoid mRNA. By analogy with ovalbumin RNA processing, these data suggest that ovomucoid mRNA is derived from a primary transcript that contains intervening sequences.

The ovalbumin gene: transcriptional regulation by estrogen

De novo synthesis of RNA sequences corresponding to intervening as well as to structural sequences of the ovalbumin gene have been detected in isolated oviduct nuclei. Their presence in the nuclear transcripts and their time course of induction support the hypothesis that transcription of structural and intervening sequences of the natural ovalbumin gene are regulated by steroid hormones. These results are in agreement with out previous demonstration of high-molecular-weight species of ovalbumin RNA in nuclei that contain structural as well as intervening RNA sequences and are thus likely precursors to mature cytoplasmic mRNAov. Analysis of the size of in vivo nuclear RNA by gel electrophoresis under denaturing conditions, revealed that withdrawal of hormone depletes the level of high molecular weight ovalbumin RNA as well as that of nature mRNAov and that readministration of estrogen induces the accumulation of both species. These results are consistent also with transcriptional regulation of the ovalbumin gene. In addition, they rule out the possibility that the rapid accumulation of mature mRNAov after secondard stimulation results from processing of ovalbumin RNA precursors that might have been stored in the withdrawn oviduct. We conclude that steroid hormones exert a primary effect at the level of gene transcription. Following this event, a series of coordinated cellular responses may occur which involve RNA processing, mRNA transport to the cytoplasm, protein synthesis and mRNA degradation. The final consequence of this network of molecular reactions is the induced cellular function inherent to a specific steroid hormone.

Effect of estrogen on gene expression in the chick oviduct. In vitro transcription of the ovalbumin gene

Problems involved in using the Hg-nucleotide technique for in vitro chromatin transcription are 2-fold. First, Escherichia coli RNA polymerase can utilize endogenous RNA as template and synthesize complementary sequences which remain base-paired to the template, thereby allowing it to bind to the SH-Sepharose column and copurify with the newly synthesized Hg-RNA. Second, non-mercurated endogenous RNA can bind to the SH-Sepharose through aggregation with Hg-RNA and thus be retained in the final RNA preparation. These two problems associated with the Hg-nucleotide technique can be minimized by modifying the conditions for RNA synthesis and SH-Sepharose chromatography. Using the modified procedure the Hg-nucleotide and SH-Sepharose technique can remove more than 90% of endogenous RNA contaminants. In order to directly demonstrate that the mRNAov sequences detected in vitro result from de novo transcription of oviduct chromatin, experiments were carried out which show that the hybridizable RNA sequences contain the Hg element and that the synthesis of these RNA sequences is sensitive to low concentrations of actinomycin D. These combined results strongly suggest that the majority of mRNAov sequences detected by hybridization to cDNAov is indeed due to DNA-dependent RNA synthesis by E. coli RNA polymerase and not due to an artifact of endogenous RNA contamination. This observation was further supported by data obtained using a filter hybridization method which measures directly the mRNAov sequences present in [3H]RNA synthesized from chromatin. The 3H-labeled ovalbumin messenger RNA was assayed by hybridization to cloned pOV230 DNA containing the ovalbumin structural gene sequence. With this modified Hg-nucleotide-SH-Sepharose technique and filter hybridization technique, we have restudied the in vitro transcription of the ovalbumin gene from chromatins isolated at different stages of hormone-induced oviduct development. The results are in agreement with our previous findings which suggest that the primary regulation of ovalbumin synthesis by steroid hormones occurs at the transcriptional level.

Transcription of structural and intervening sequences in the ovalbumin gene and identification of potential ovalbumin mRNA precursors

Structural sequences that are extensively separated by nonstructural intervening sequences in the natural ovalbumin gene are coordinately expressed in target and nontarget tissue. The intervening sequences, which consist of unique sequences in the chick genome, are transcribed in their entirety. The amount of nuclear RNA corresponding to these sequences, however, is approximately 10 times less than that observed for structural sequences. The accumulation of RNA corresponding to structural and intervening sequences during acute estrogen stimulation suggests either that there are different rates of transcription for these regions of the ovalbumin gene or that RNA sequences corresponding to the intervening sequences are preferentially processed and degraded. Comparison of the in vitro expression of portions of the ovalbumin gene in nuclei isolated from chronically stimulated oviducts indicates that both structural and intervening sequences are preferentially transcribed in vitro at rates approximately 500 times greater than expected for random transcription of the haploid chick genome. In addition, electrophoresis of oviduct nuclear RNA on agarose gels containing methylmercury hydroxide reveals multiple species of RNA that are from 1.3 to over 4 times larger than ovalbumin mRNA and hybridize to both structural and intervening sequences of the ovalbumin gene. These results are consistent with transcription of the entire ovalbumin gene into a large precursor molecule followed by excision of the intervening sequences and appropriate ligation of the structural sequences to form the mature mRNA.

Regulation of translation of ovalbumin messenger RNA by estrogens and progesterone in oviduct of withdrawn chicks

In the oviduct of chicks withdrawn from previous treatment with estrogens, no ovalbumin synthesis can be detected, although there are a limited number of ovalbumin mRNA sequences. These sequences are predominately associated with membrane-bound ribosomes. However, the size of the polysomes is small compared to those from the laying hen, suggesting that the inability to detect ovalbumin synthesis is the result of inefficient initiation of ovalbumin synthesis. When the rate of peptide chain elongation is reduced by treatment of chicks with cycloheximide, there is an increase in the average size of polysomes and a shift of ovalbumin mRNA sequences from small to large-sized polysomes. Readministration of estrogen to withdrawn chicks results in a time-dependent shift of monosomes to polysomes and a proportional shift of ovalbumin mRNA sequences between the two fractions, indicating that estrogen stimulates the rate of initiation of all mRNA species in the oviduct to essentially the same extent. In contrast, progesterone administration results in a preferential shift of ovalbumin mRNA relative to total RNA, suggesting a preferential effect of progesterone on initiation of protein synthesis with ovalbumin mRNA.

Cloning of chicken lysozyme structural gene sequences synthesized in vitro

Double-stranded chicken lysozyme cDNA was synthesized from an oviduct mRNA fraction enriched for lysozyme mRNA. The ds-cDNA was inserted into the BamHI site of plasmid pBR322 using chemically synthesized DNA linker molecules containing the BamHI restriction endonuclease cleavage site. After bacterial transformation, colonies carrying lysozyme DNA were identified by hybridization with highly purified lysozyme cDNA. The 555 base pairs long cloned DNA fragment of one recombinant plasmid was isolated and characterized by restriction endonuclease digestion. The DNA sequence of selected parts of the inserted DNA is as predicted from the amino acid sequence of prelysozyme. The sequence data allows the unambiguous location of the coding region within lysozyme mRNA.

Effects of testosterone on messenger ribonucleic acid and protein synthesis in rat seminal vesicle

In a previous report [Higgins et al. (1976) Biochem. J.158, 271-282] we described the effects of alterations in androgen status on the synthesis of two basic secretory proteins of the rat seminal vesicle. In the present paper we examine the effects of testosterone on the activity of mRNA in the seminal vesicle. Total cellular poly(A)-rich RNA was isolated and translated in a cell-free system prepared from wheat germ. Translation products were separated on denaturing polyacrylamide gels and the protein bands corresponding to the two basic secretory proteins were identified immunologically. Incorporation of radioactive methionine into these bands was taken as a measure of the individual mRNA activities. Total mRNA activity was estimated by radioactivity in total acid-precipitable material. The results show that 1 to 2 weeks after castration the activities of mRNA molecules for the basic secretory proteins were decreased 10-20-fold on a tissue basis. Testosterone given in vivo rapidly and substantially restores mRNA activity to normal. Since these changes correlate closely with variations in the rates of synthesis of the secretory proteins in whole cells it suggests that androgenic steroids control protein synthesis chiefly via mRNA availability. In this respect their action resembles those of other steroid hormones acting in other systems. However, these effects of testosterone on the mRNA molecules for the major secretory proteins could not be distinguished from those on total mRNA. Thus the proportion of the total mRNA population accounted for by the two specific mRNA molecules showed less than a 2-fold variation with androgen status. Similarly the two secretory proteins always accounted for 25-33% of general protein synthesis. This is in sharp contrast with the markedly differential effects of other steroid hormones controlling synthesis of major proteins in other well-studied systems. We interpret our results as indicating that testosterone regulates the mRNA population of the seminal vesicle as a whole.

Differential transcription of nonrepeated DNAs in Neurospora crassa mutants

Transcriptional properties of an "albino" mutant, a "slime" mutant and a wild type strain of Neurospora crassa have been compared by quantitative estimates of DNA:RNA hybridization. The RNAs isolated from these strains were incubated with 32P-DNA of the wild type strain. The DNA:RNA hybrids were isolated by chromatography on hydroxyapatite. 29--34% of the wild type 32P-DNA hybridized with RNA from all of the strains used. The DNA sequences which gave a primary reaction with wild type RNA (tr-DNA) were recovered and again reacted with different RNAs. The tr-DNA sequences reacted to the extent of 92% with the wild type RNA, but only 78% with slime mutant RNA and 85% with the RNA isolated from the albino mutant. The use of tr-DNA sequences thus isolated, proved to have increased the specificity of the hybridization reactions, these were useful indicators for identification of transcriptional differences among wild type and mutant strains of N. crassa.

The concept of mRNA abundance classes: a critical reevaluation

Derivative plots have been constructed for hybridization reactions between polysomal poly(A)-containing RNA and oligo(dT)-primed cDNA. In one method the derivative was calculated directly from the data, and in the other, from a non-linear least squares fit using 9-10 ideal components. In some cases these methods yield very similar results and strongly suggest that the hybridization data support discrete components. Reactions with two and four major components indicate that the often-reported three abundance class model is only one of several possibilities for eukaryotic cells. In other situations neither method strongly suggests the presence of discrete components (in one case even after enrichment of the cDNA population by kinetic fractionation), implying that the components are closely spaced or that the entire mRNA population of those cells may not exist as discrete abundance classes. The universal occurrence of discrete abundance classes should be critically reexamined.

Hormonal control of mRNA synthesis studied by nucleic acid hybridization

The regulation of protein synthesis by steroids is thought to be due to hormonal effects primarily on mRNA concentration. Experimental evidence to support this conclusion has come largely from the use of DNA probes complementary (cDNA) to mRNA molecules or by translation of the mRNA in vitro. In this review the experimental procedures involved and the application to hormone action of cDNA hybridization will be reviewed. (1) mRNA concentrations can be assayed in tissue RNA samples by hybridization with radiolabelled complementary DNA probes (cDNA). From the rate of hybridization of an mRNA preparation to a cDNA probe it is possible to estimate specific mRNA concentrations and thereby study their hormonal regulation within tissues of subcellular fractions (2) Rates of synthesis of a specific RNA can be measured by hybridization of pulse-labelled RNA with excess cold cDNA as illustrated in studies of the glucocorticoid induction of MMTV RNA. (3) Hormore-induced alterations of mRNA populations as a whole can be investigated. From the kinetics of hybridization of mRNA with its complementary DNA it is possible to estimate the number of different RNA sequences in tissues and to approximate the number of copies of each sequence per cell. Consequently, by comparing mRNA samples isolated from tissues of different hormonal status it is possible to demonstrate specific hormone-inducible mRNA species and, in some cases, identify their translation products.

Reverse transcription of thyroglobulin 33-S mRNA

Bovine thyroglobulin 33-S mRNA has been used as a template for the synthesis of a complementary DNA, using RNA-directed DNA polymerase from the avian myeloblastosis virus. The yield of the reaction was relatively poor and the size of the cDNA did not exceed 10 S. Nevertheless, a copy of high specific radioactivity (approximately 10(7) counts. min-1 microgram-1) could be obtained which hybridized specifically back to its template with an rot1/2 value about 5 times higher than that observed in hybridizations between hemoglobin mRNA (alpha + beta chain) and hemoglobin cDNA. This suggests that thyroglobulin mRNA does not contain extensive internal repetitive sequences. Quantification of thyroglobulin mRNA sequences among various RNA preparations from the beef thyroid was performed using cDNA/RNA hybridizations in RNA excess. The results confirmed that thyroglobulin mRNA represents the large majority of mRNA in membrane-bound polysomes and indicated the virtual absence of thyroglobulin sequences on free polyosomes. The cDNA transcribed from mRNA of bovine origin hybridized efficiently with thyroid RNA from goats, dogs and humans. Although the heterologuous hybrids exhibited the expected decrease in thermal stability, the bovine cDNA provides an appropriate probe for studies dealing with the expression of the thyroglobulin gene in various mammals including man.