Vascular smooth muscle calponin. A novel troponin T-like protein

In a search for additional Ca2+ regulatory components in vascular smooth muscle, a novel troponin T-like protein was purified from bovine aorta smooth muscle. The isolated protein was separated into several isoforms on isoelectric focusing. The major isoelectric variants were focused in the pH region of 8.4 to 9.1. The protein had slightly different molecular masses in the Mr range of 35,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Its molar ratio relative to tropomyosin in the muscle extract was estimated to be 0.9:1.0. The novel protein bound to the immobilized calmodulin and exhibited a number of common physicochemical properties with gizzard (Mr = 34,000) calmodulin-binding and F-actin-binding protein. The aorta and gizzard proteins were immunologically cross-reactive. Both proteins shared a common antigenic determinant with COOH-terminal segments of rabbit skeletal and bovine cardiac troponin T and bound to the immobilized smooth muscle tropomyosin. Both proteins interacted with rabbit skeletal troponin C in the presence and absence of Ca2+, but they did not interact with troponin I. These results suggest that the novel protein, which is designated calponin, may be a specialized component of smooth muscle thin filament involved in the regulation of contractile apparatus.

Isolation and purification of an antibody to 67-KD calcimedin

The 67-KD calcimedin is a calcium-binding protein isolated from several muscle tissues. The protein shows apparent Mr of 67,000 by SDS-polyacrylamide gel electrophoresis. An antibody has been prepared by immunizing sheep with the protein purified from chicken gizzard smooth muscle. This antibody recognizes 67-KD calcimedin but not calmodulin, bovine serum albumin, transferrin, or brain p68 calelectrin. The presence of 67-KD calcimedin is demonstrated in the smooth muscle cell lines A10 and DDT1MF-2 as well as in primary cultures of chicken breast and heart muscle, by immunoprecipitation and immunofluorescence. The 67-KD calcimedin, being responsive to calcium, may play a role in calcium-mediated cell regulation. This report identifies several cells that may be useful for further delineation of the cellular role of 67-KD calcimedin.

A histochemical study of the mucins in the digestive tract of the chicken

Little is known about the distribution of glycoproteins in the digestive tube of birds. In the present study, the localization and distribution of mucins in the digestive tract of the chicken are reported. Sialo- and sulpho-mucins were widely distributed throughout the chicken digestive tube. Some of the mucous cells of the proximal segment of the proventriculus presented neutral glycoproteins; in the medial segment, surface cells containing only sialo-mucins were observed. Surface cells of the gizzard contained both sialo- and sulpho-mucins while PAS-positive material was localized in the lumen of the glands. 2 types of mucous cells were observed in the small intestine; 1 type contained only sialo-mucins and the other contained both sialo- and sulpho-mucins. In the large intestine and caecum, both types of acid mucins were present in the mucous cells. In conclusion, the distribution of glycoproteins in the chicken reported in the present study show marked differences with that reported in other avian species.

Wide variation of myoglobin contents in gizzard smooth muscles of various avian species

We determined myoglobin contents of gizzards (muscular stomach) and breast muscles in 34 avian species by a modification of Reynafarje's spectrophotometric procedure. The birds were apparently differentiated into two groups in respect of the gizzard, one with a high myoglobin content (7.74 +/- 1.81 mg/g muscle) and the other with a low (1.54 +/- 0.41 mg/g). In the former group of 15 species all but one were herbivorous, and all but one were carnivorous or else omnivorous in the latter group of 19 species. The myoglobin level was considered to closely correlate with mechanical performance and therefore oxygen demands of the gizzards. It might also be relevant to a circulatory situation during the tonic contractions of this organs.

Characteristic structures of actin gels induced with hepatic actinogelin or with chicken gizzard alpha-actinin: implication for their function

We studied the properties of actinogelin, a Ca2+-regulated actin cross-linking protein isolated from Ehrlich tumor cells or rat liver. Chicken gizzard alpha-actinin was used as a Ca2+-insensitive control. Actinogelin, which has very high gelation activity under low Ca2+ conditions, was found using electron microscopic or fluorescence studies to induce formation of a characteristic structure in which actin filaments and bundles radiate to (or converge from) all directions from spot-like core structures. A similar structure was induced with actinogelin, even in the presence of 0.7 saturation of tropomyosin. No such structure was detected with actinogelin under high Ca2+ conditions, and only a few were found with gizzard alpha-actinin. Because reconstituted structures are similar to those observed intracellularly, actinogelin may be important in the formation of similar microfilament organization in the cells. It seems also important that these structures are reconstituted with only two purified protein components, i.e., actinogelin and actin. Immunocompetition studies showed that actinogelin and gizzard alpha-actinin partially shared antigenicity, and their molecular shape and peptide maps were similar. Their amino acid compositions [Kuo et al., 1982], subunit and domain structures, and binding sites on actin [Mimura and Asano, 1987] are also very similar. Therefore, it is concluded that actinogelin belongs to alpha-actinin superfamily proteins. Furthermore, the presence of functionally different subfamilies concerned with Ca2+ sensitivity, gelation-efficiency, and others is discussed. Actinogelin, which induces networks of actin filaments, may be classified as high gelation type.

The effect of caldesmon on actin-myosin interaction in skeletal muscle fibers

The effects of caldesmon on structural and dynamic properties of phalloidin-rhodamine-labeled F-actin in single skeletal muscle fibers were investigated by polarized microphotometry. The binding of caldesmon to F-actin in glycerinated fibers reduced the alterations of thin filaments structure and dynamics that occur upon the transition of the fibers from rigor to relaxing conditions. In fibers devoid of myosin and regulatory proteins (ghost fibers) the binding of caldesmon to F-actin precluded structural changes in actin filaments induced by skeletal muscle myosin subfragment 1 and smooth muscle tropomyosin. These results suggest that the restraint for the alteration of actin structure and dynamics upon binding of myosin heads and/or tropomyosin evoked by caldesmon can be related to its inhibitory effect on actin-myosin interaction.

Yeast calmodulin: structural and functional differences compared with vertebrate calmodulin

Calmodulin of the baker's yeast (Saccharomyces cerevisiae) showed a similar affinity for Ca2+ to that of vertebrate calmodulin. The maximum binding number of Ca2+ to yeast calmodulin was, however, 3 mol/mol, which is lower than that of vertebrate calmodulin (4 mol/mol). The same maximum activity of porcine brain phosphodiesterase was attained when 100 times higher concentration of yeast calmodulin than that of vertebrate calmodulin was added. On the other hand, the maximum activation of chicken gizzard myosin light chain kinase was attained with 1,000 times higher concentration of yeast calmodulin than that of vertebrate calmodulin, and the maximum activity with yeast calmodulin was less than 1/5 of that with vertebrate calmodulin. Several amino acid substitutions observed in the yeast calmodulin, particularly at the alpha-helical rod connecting the two globular domains, may affect the interaction mode of various target enzymes with this calmodulin.

A chicken embryo-specific myosin light chain (L23) appears to be identical with one of brain myosin light chains

A novel embryo-specific myosin light chain of 23 kDa molecular weight (L23) was found previously in embryonic chicken skeletal, cardiac, and smooth muscles (Takano-Ohmuro et al. (1985) J. Cell Biol. 100, 2025-2030). When we examined myosin in embryonic and adult brain by two-dimensional electrophoresis, 23 kDa myosin light chain present in brain (Burridge & Bray (1975) J. Mol. Biol. 99, 1-14) comigrated with L23. Two monoclonal antibodies, EL-64 and MT-185d, were applied to clarify the identity of the brain 23 kDa myosin light chain and the chicken embryonic muscle L23. The two antibodies recognize different antigenic determinants in the L23 molecule; the former antibody is specific for L23, whereas the latter recognizes the sequence common to fast skeletal muscle myosin light chains 1 and 3, and also L23. The immunoblots combined with two-dimensional gel electrophoresis showed that both EL-64 and MT-185d can bind to the brain 23 kDa myosin light chain as well as the chicken embryonic muscle L23. These results indicate that chicken brain and chicken embryonic muscles contain a common myosin light chain of 23 kDa molecular weight.

Isolation and characterization of a calmodulin binding fragment of chicken gizzard caldesmon

A calmodulin binding portion was separated from chicken gizzard caldesmon by chymotryptic digestion and it was purified through two column chromatography steps on calmodulin-Sepharose and Ultrogel AcA 44. The isolated fragment has an estimated molecular weight of 35,000 (35K) and it was possibly derived from the C-terminal portion of caldesmon. The affinity of the 35K fragment for calmodulin was determined by using the characteristic calmodulin-dependent mobility shift in polyacrylamide gel electrophoresis. The 35K fragment retained the actin binding site of caldesmon. The interaction of the 35K fragment with actin was released in the presence of Ca2+ and calmodulin.

Interaction of monoclonal antibodies with a neurite outgrowth factor from chicken gizzard extract

A neurite outgrowth factor (NOF), which promotes neurite outgrowth of cultured peripheral neurons, was purified to homogeneity from chicken gizzard extract and used as an immunogen for generating monoclonal antibodies. From 603 hybridoma clones, 55 positive hybridoma cell lines were detected. Four of them (IgG1 (kappa-chain) producers designated as 5-10A, M1-2G, 4-2C and 1-4D) were selected for further characterization. These antibodies immunoprecipitated 125I-labelled gizzard NOF molecules, whereas they did not inhibit the biological activity of NOF (or NOF-like molecules) derived from the tissues tested. The subcellular distribution of NOF in chick embryonal tissues was investigated using monoclonal antibody 4-2C. Both ciliary ganglionic (CG) neurons and gizzard muscle tissues were stained. The NOF content of embryonic CG, measured by an immunoblot assay, increased about 20-fold during embryogenesis from 6 to 15 days, whereas the sensitivity of neurons to NOF reciprocally decreased. At least two different sizes of NOFs (700 and 800 kDa) were found in CG of various ages, with the 800/700 kDa ratio gradually increasing with age. A mixture of these 4 monoclonal antibodies was used for immunoaffinity purification of NOF from chicken gizzard muscles.

Withdrawal of zinc oxide-containing diets from mature, female domestic fowl: effects on selected tissue mineral contents

1. Two hundred and sixteen laying hens of two strains were given diets containing ZnO to provide 0, 0.5, 0.75, 1.00, 1.25, 1.50, 2.00, 3.00 or 4.00 g added Zn/kg. These diets were offered ad libitum for 5 consecutive 28-d periods. All hens were subsequently offered the control diet with no added ZnO for 5 weeks. 2. Four hens from each treatment were killed 0, 1 and 5 weeks after substitution of the ZnO-supplemented diets by the control diet. 3. Dietary addition of ZnO significantly increased liver, kidneys, pancreas and gizzard Zn contents but this effect was rapidly reversed on removal of the ZnO-containing diets. 4. Hepatic and renal Fe contents were significantly depressed by dietary ZnO but after substitution of these diets by the control diet the values were comparable to that of the controls. 5. Liver Cu content declined significantly as dietary ZnO concentration increased but there was a return towards normal after ZnO withdrawal. Renal, pancreatic and gizzard Cu contents showed quadratic responses to added ZnO. 6. After ZnO withdrawal for 5 weeks, pancreas Cu contents declined linearly, whereas renal and gizzard Cu values were similar for all treatments. 7. Overall the long-term feeding of ZnO-supplemented diets followed by a period of withdrawal of the ZnO supplement had no detrimental effects on tissue mineral contents.

Type VI collagen represents a major fraction of connective tissue collagens

A new method for the isolation of type VI collagen from peptic tissue digests is presented which gives tenfold higher yields than methods previously reported. From the amounts of purified protein obtained from human placenta, bovine uterus, chicken gizzard and entire mouse bodies we conclude that type VI collagen represents a major fraction of connective tissue collagens.

Specific interaction of vinculin with alpha-actinin

Vinculin and alpha-actinin are cytoskeletal proteins present at focal contacts of the ventral surface of cultured fibroblasts. We labelled alpha-actinin with an acceptor fluorophore and vinculin with a donor. A mixture of vinculin and alpha-actinin showed a 28% quench, due to energy transfer, suggesting an interaction. Quench of vinculin was dependent on the concentration of alpha-actinin; Scatchard analysis gives a dissociation constant in the microM range. Quench was inhibited by excess unlabelled alpha-actinin, and by reaction of the acceptor protein with p-chloromercuribenzoate. We found that vinculin had a slightly greater elution volume in a gel filtration column equilibrated with alpha-actinin, indicating a higher effective Stokes radius due to the interaction of the two proteins.

Diversity in smooth muscle thin filament composition

Two classes of smooth muscle thin filament can be identified and separated based on their interaction with antibodies specific either to filamin or to caldesmon. One type is composed of actin, tropomyosin and filamin and the other of actin, tropomyosin and caldesmon.

Occurrence of anti-gizzard P34K antibody cross-reactive components in bovine smooth muscles and non-smooth muscle tissues

In our previous paper (Biochem. Biophys. Res. Commun. 141, 20-26 (1986) we reported the isolation of a 34000-dalton protein (p34K) which binds to calmodulin and F-actin from chicken gizzard smooth muscle. We examined the distribution of the immunoreactive component of gizzard p34K in bovine tissues by immunoblot analysis using a rabbit polyclonal antibody raised against gizzard p34K. The immunoreactive components with molecular weights of 33000-35000 were detected in all smooth muscles from aorta, esophagus, stomach, trachea and uterus. In non-smooth muscle tissues, a 36000-dalton cross-reactive protein was present in adrenal medulla and cortex. The immunoreactive form of gizzard p34K occurred in large amounts in smooth muscles from various bovine tissues.

Properties of talin from chicken gizzard smooth muscle

This paper describes the structural and biochemical characterization of talin, a protein localized to various cellular sites where bundles of actin filaments attach to the plasma membrane. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the protein has a molecular mass of 225,000 +/- 5,000 daltons. Hydrodynamic measurements at protein concentrations less than 0.72 mg/ml indicate a monomeric protein with a native molecular mass of 213,000 +/- 15,000 daltons. Sedimentation equilibrium experiments indicate self-association at protein concentrations of 0.72 mg/ml and higher. The data suggest that this self-association is a simple monomer:dimer equilibrium over the range of concentrations observed. At low protein concentrations where talin is a monomer, the Stokes radius and sedimentation coefficient vary with ionic strength. Under low ionic strength conditions (5-20 mM NaCl), talin has a Stokes radius of 6.5 nm and a sedimentation value of 9.4, suggesting an asymmetric globular molecule; whereas under high ionic strength conditions (200 mM NaCl), the Stokes radius increases to 7.7 nm and the sedimentation coefficient decreases to 8.8, suggesting a more elongated protein. This conformation change is confirmed by electron microscopy which reveals a more globular protein at low ionic strength which unfolds to become an elongated flexible molecule as the ionic strength is increased to physiological and higher levels. The amino acid composition of talin indicates a low level of aromatic residues, consistent with its relatively low extinction coefficient, talin has an isoelectric point between pH 6.7 and 6.8 based on isoelectric focusing. The detailed purification of talin is described.

Smooth muscle caldesmon is an extended flexible monomeric protein in solution that can readily undergo reversible intra- and intermolecular sulfhydryl cross-linking. A mechanism for caldesmon's F-actin bundling activity

Caldesmon is a major F-actin binding protein of smooth muscle that has been implicated as a component of a thin filament regulatory system. Chicken gizzard caldesmon consists of polypeptides of Mr-135,000 and 140,000 which are closely related as determined by analysis of cyanogen bromide cleavage fragments. It is a highly extended flexible protein having a contour length of about 146 nm and a secondary structure composed primarily of random coil. Physical and chemical cross-linking data suggest that caldesmon exists as a monomer in solution. The cysteine content of caldesmon was determined to be 2 residues/polypeptide. Remarkably, in solution it readily undergoes sulfhydryl oxidation to form either an internal disulfide bridge in the protein or cross-links between individual polypeptides to form dimers, trimers, tetramers, etc. The internally cross-linked species have a smaller Stokes radius than the reduced molecules, indicating that the cross-link "trapped" the molecule in a compact conformation. Oxidized protein containing caldesmon oligomers is a potent F-actin bundling protein. Complete reduction of caldesmon abolishes the F-actin bundling activity. Since a vast excess of reducing agent is required to convert caldesmon from an oxidized to reduced state, it may exist in either state in vivo. Thus, the ability of caldesmon to undergo reversible sulfhydryl cross-linking, and thereby reversible F-actin cross-linking, may be of physiological significance.

Amino acid sequence of chicken gizzard smooth muscle SM22 alpha

The complete amino acid sequence of SM22 alpha, a novel and abundant 22-kDa protein from chicken gizzard smooth muscle, was determined by a combination of automated and manual Edman degradation methods on fragments produced by suitable chemical and proteolytic cleavages. The protein consists of a single polypeptide chain of 197 residues, has a Mr of 21, 978, and a net charge of +4.5 at neutral pH. The pattern of alternating hydrophilic and hydrophobic regions throughout the length of SM23 alpha is typical of a globular protein. The overall secondary structural analysis, using several algorithms based on the sequence, predicts approximately 31% alpha-helix, 24% beta-sheet, 18% beta-turn, and 27% random coil. A search against the National Biomedical Research Foundation Protein Sequence Databank (Washington) and GenBank (Los Alamos) failed to demonstrate significant similarity with any other protein of known sequence.

High-performance liquid chromatography of amino acids, peptides and proteins. LXIX. Evaluation of retention and bandwidth relationships of myosin-related peptides separated by gradient elution reversed-phase high-performance liquid chromatography

The gradient elution behaviour of ten peptide analogues encompassing the primary amino acid sequences adjacent to the serine-19 phosphorylation site of myosin light chain has been investigated using a 30-nm pore diameter n-butylsilica stationary phase and 0.1% trifluoroacetic acid-water-acetonitrile mobile phases. Quantitative expressions derived from linear solvent strength theory and general plate height theory have been used to assess the influence of gradient time and flow-rate on the relative retentions and bandwidths of these peptides. The retention behaviour of these peptide analogues was found to closely mirror the predictions of linear solvent strength gradient elution theory. Although the experimentally observed band-width changes over a conventional range of gradient conditions (i.e. tG = 30-60 min) also correlated with bandwidth changes predicted on the basis of plate theory derived for low molecular weight organic molecules, for very steep and very shallow gradients divergencies from theory were observed. The significance of these discrepancies is discussed in relation to the influence of amino acid sequence changes rather than composition of these peptide analogues. These data allow the importance of sequential effects on the chromatographic behaviour and in particular, the resolution optimisation of these closely related peptides to be evaluated.

Activation of smooth muscle myosin Mg2+-ATPase by native thin filaments and actin/tropomyosin

Application of the myosin competition test (Lehman, W., and Szent-Györgyi, A. G. (1975) J. Gen. Physiol. 66, 1-30) to chicken gizzard actomyosin indicated that this smooth muscle contains a thin filament-linked regulatory mechanism. Chicken gizzard thin filaments, isolated as described previously (Marston, S. B., and Lehman, W. (1985) Biochem. J. 231, 517-522), consisted almost exclusively of actin, tropomyosin, caldesmon, and an unidentified 32-kilodalton polypeptide in molar ratios of 1:1/6:1/26:1/17, respectively. When reconstituted with phosphorylated gizzard myosin, these thin filaments conferred Ca2+ sensitivity (67.8 +/- 2.1%; n = 5) on the myosin Mg2+-ATPase. On the other hand, no Ca2+ sensitivity of the myosin Mg2+-ATPase was observed when purified gizzard actin or actin plus tropomyosin was reconstituted with phosphorylated gizzard myosin. Native thin filaments were rendered essentially free of caldesmon and the 32-kilodalton polypeptide by extraction with 25 mM MgCl2. When reconstituted with phosphorylated gizzard myosin, caldesmon-free thin filaments and native thin filaments exhibited approximately the same Ca2+ sensitivity (45.1 and 42.7%, respectively). The observed Ca2+ sensitivity appears, therefore, not to be due to caldesmon. Only trace amounts of two Ca2+-binding proteins could be detected in native thin filaments. These were identified as calmodulin (present at a molar ratio to actin of 1:733) and the 20-kilodalton light chain of myosin (present at a molar ratio to actin of 1:270). The Ca2+ sensitivity observed in an in vitro system reconstituted from gizzard thin filaments and either skeletal myosin or phosphorylated gizzard myosin is due, therefore, to calmodulin and/or an unidentified minor protein component of the thin filaments which may be an actin-binding protein involved in regulating actin filament structure in a Ca2+-dependent manner.

The tissue form of chicken type VI collagen

We have purified intact type VI collagen from chicken gizzard. The protein was found to consist of a 130 kDa, a 140 kDa and a 180-200 kDa subunit. The 130 kDa and 140 kDa subunits were obtained in equimolar amounts and identified as the alpha 2 (VI) and the alpha 1 (VI) chains, respectively. The third subunit was usually obtained in the form of 3-4 closely related polypeptides, which may represent different processing or modification products of the alpha 3 (VI) chain.

Properties of smooth muscle meta-vinculin

Quantitative studies show that meta-vinculin is ninefold more soluble in 0.6 M salt than in the 0.01 M salt buffers used to extract vinculin. Based on this finding, we have developed a protocol for the purification of meta-vinculin in 43% yield and 98% purity from a high salt extract of gizzard smooth muscle. In contrast to our earlier extraction studies, which were done on unfixed cryostat sections (30), the present studies done on tissue homogenates show that nonionic detergents are not required for solubilization of meta-vinculin. Furthermore, neither purified nor partially purified meta-vinculin binds to Triton X-114 micelles. Purified meta-vinculin is a monomeric, asymmetric molecule with a Stokes radius of 50.9 A, a sedimentation coefficient of 6.35S, and a frictional ratio of 1.46. The calculated molecular weight of meta-vinculin is 145,000. Meta-vinculin has two isoforms of pI 5.9 and 6.2, and is phosphorylated in vivo to eightfold greater specific activity than vinculin. On immunoblots of smooth muscle proteins, [125I]meta-vinculin binds specifically to talin and also to unidentified polypeptides of 180, 150, 95, 70, 68, and 45 kD. On two-dimensional peptide maps, iodinated vinculin and meta-vinculin have at least 95% of their major chymotryptic peptides in common, but each protein also has at least one highly labeled peptide that appears to be unique. Comparative peptide maps of high salt soluble meta-vinculin and the low salt soluble 152-kD protein (described by Feramisco, J.R., J.E. Smart, K. Burridge, D. Helfman, and G.P. Thomas, 1982, J. Biol. Chem., 257:11024-11031) demonstrate extensive similarities among the vinculin-like proteins but suggest a lack of complete identity. In vivo pulse-chase experiments show that meta-vinculin and vinculin do not have a precursor-product relationship. The biochemical and structural differences found between vinculin and meta-vinculin suggest that there is a unique function for meta-vinculin in smooth muscle.

Domain mapping of chicken gizzard caldesmon

Limited proteolysis, affinity chromatography, and immunoblotting have been used to define the domains of chicken gizzard caldesmon, caldesmon120, that interact with calmodulin, F-actin, and a monoclonal antibody prepared using human platelet caldesmon. Treatment of caldesmon120 with chymotrypsin produces groups of fragments near 100, 80, 60, 38, and 20 kDa. Further digestion produces peptides between 40 and 50 kDa. The 100- and 80-kDa peptides cross-react with the monoclonal antibody; the smaller polypeptides do not. The kinetics of cleavage and the antibody studies indicate that the 38- and 80-kDa fragments are the two major pieces of the 120-kDa protein. The 38-kDa fragment, purified by high performance liquid chromatography, and several of its subfragments at 21 and 25 kDa sediment with F-actin, bind to calmodulin-Sepharose in the presence of Ca2+, and are displaced from F-actin by Ca2+-calmodulin. The 80-kDa fragments did not interact with F-actin or calmodulin. We have tentatively placed the 38-kDa fragment at the C-terminal using polyclonal antibodies selected against a beta-galactosidase-caldesmon120 fusion protein produced by a lambda gt11 lysogen. The 38-, 25-, and 21-kDa fragments cross-react with these antibodies; the 80- and 60-kDa fragments do not. Caldesmon77 from human platelets also cross-reacts with these selected antibodies. The results suggest that interacting calmodulin and F-actin binding sites are localized on a 38-kDa C-terminal fragment of caldesmon. The smallest subfragment of this peptide that binds to both F-actin and calmodulin-Sepharose is about 21 kDa. The monoclonal antibody epitope is tentatively localized near the N-terminal of caldesmon77 and must be within 50 kDa of the N-terminal on caldesmon120.

Hormonal regulation of a chicken oviduct messenger ribonucleic acid that shares a common domain with gizzard myosin light chain kinase

Changes in myosin light chain kinase (MLCK) and calmodulin (CaM) mRNAs have been evaluated during estrogen-mediated differentiation of the chicken oviduct. Also examined were acute changes that occur in oviduct RNA from animals stimulated with estrogen, withdrawn from hormone and then injected for 1, 2, and 4 days with synthetic estrogen [diethylstilbestrol (DES)], progesterone (P), or testosterone (T). Small changes were noted in both CaM and MLCK RNAs during primary stimulation when oviduct cells are actively dividing. On the other hand no significant changes were observed during secondary stimulation regardless of the steroid hormone injected. These data support the contention that CaM and MLCK are constitutively expressed but vary as a function of cell cycle. The MLCK mRNA is 5.5 kilobases (kb) but the MLCK cDNA also hybridizes to an oviduct RNA 2.7 kb long. This RNA species is acutely regulated by estrogen, P, and T but in a manner different from that of ovalbumin mRNA. The magnitude of stimulation of the 2.7 kb mRNA by diethylstilbestrol and T is greater than that of ovalbumin whereas changes in response to P are similar. The 12- to 16-fold increase of the 2.7 kb mRNA in response to T is the largest effect reported for this hormone acting on oviduct. The 2.7 kb mRNA encodes an unknown protein yet contains a 520 nucleotide segment that is highly homologous with the COOH-terminal coding portion of the MLCK mRNA. Since this homology does not include either catalytic or CaM-binding domains of MLCK, it is unlikely that the 2.7 kb mRNA encodes a CaM-dependent protein kinase.(ABSTRACT TRUNCATED AT 250 WORDS)