The amino acid sequence of the Tetrahymena calmodulin which specifically interacts with guanylate cyclase

Calmodulin in Paramecium: Focus on Genomic Data

Calcium (Ca²⁺) is a universal second messenger that plays a key role in cellular signaling. However, Ca²⁺ signals are transduced with the help of Ca²⁺-binding proteins, which serve as sensors, transducers, and elicitors. Among the collection of these Ca²⁺-binding proteins, calmodulin (CaM) emerged as the prototypical model in eukaryotic cells. This is a small protein that binds four Ca²⁺ ions and whose functions are multiple, controlling many essential aspects of cell physiology. CaM is universally distributed in eukaryotes, from multicellular organisms, such as human and land plants, to unicellular microorganisms, such as yeasts and ciliates. Here, we review most of the information gathered on CaM in Paramecium, a group of ciliates. We condense the information here by mentioning that mature Paramecium CaM is a 148 amino acid-long protein codified by a single gene, as in other eukaryotic microorganisms. In these ciliates, the protein is notoriously localized and regulates cilia function and can stimulate the activity of some enzymes. When Paramecium CaM is mutated, cells show flawed locomotion and/or exocytosis. We further widen this and additional information in the text, focusing on genomic data.

Calmodulin-binding proteins: A journey of 40 years

The proteins which bind to calmodulin in a Ca²⁺-dependent and reversible manner are known as calmodulin-binding proteins. These proteins are involved in a multitude of processes in which Ca²⁺ and calmodulin play crucial roles. Our group elucidated the mechanism and importance of these proteins in normal and diseased conditions. Various calmodulin-binding proteins were discovered and purified from bovine tissue including a heat stable calmodulin-binding protein 70, calmodulin-dependent protein kinase VI and a high molecular weight calmodulin-binding protein (HMWCaMBP). We observed a complex interplay occurs between these and other Ca²⁺ and calmodulin-binding proteins during cardiac ischemia and reperfusion. Purified cardiac HMWCaMBP is a homolog form of calpastatin and an inhibitor of the Ca²⁺-activated cysteine proteases, calpains and therefore can have cardioprotective role in ischemic conditions. Calcineurin is a Ca²⁺ and calmodulin-dependent serine/threonine protein phosphatase showed increased phosphatase activity in ischemic heart through its direct interaction with Hsp70 and expression of calcineurin following ischemia suggests self-repair and favorable survival outcomes. Calcineurin was also found to be present in other tissues including the eye; where its expression and calcineurin phosphatase activity varied. In neurons, calcineurin may play a key role in initiating apoptosis-related pathways especially in epilepsy. In colorectal cancer we demonstrated high calcineurin phosphatase activity and simultaneous overexpression of calcineurin. The impact of calcineurin signaling on neuronal apoptosis in epilepsy and its use as a diagnostic marker for colorectal cancer requires in-depth study.

7 Non-histone protein lysine methyltransferases: Structure and catalytic roles

Non-histone protein lysine methyltransferases (PKMTs) represent an exceptionally diverse and large group of PKMTs. Even accepting the possibility of multiple protein substrates, if the number of different proteins with methylated lysyl residues and the number of residues modified is indicative of individual PKMTs there are well over a hundred uncharacterized PKMTs. Astoundingly, only a handful of PKMTs have been studied, and of these only a few with identifiable and well-characterized structure and biochemical properties. Four representative PKMTs responsible for trimethyllysyl residues in ribosomal protein LI 1, calmodulin, cytochrome c, and Rubisco are herein examined for enzymological properties, polypeptide substrate specificity, functional significance, and structural characteristics. Although representative of non-histone PKMTs, and enzymes for whichcollectively there is a large amount of information, individually each of the PKMTs discussed in this chapter suffers from a lack of at least some critical information. Other than the obvious commonality in the AdoMet substrate cofactor and methyl group transfer, these enzymes do not have common structural features, polypeptide substrate specificity, or protein sequence. However, there may be a commonality that supports the hypothesis that methylated lysyl residues act as global determinants regulating specific protein-protein interactions.

Intron Analyses Reveal Multiple Calmodulin Copies in Littorina

Intron 3 and the flanking exons of the calmodulin gene have been amplified, cloned, and sequenced from 18 members of the gastropod genus Littorina. From the 48 sequences, at least five different gene copies have been identified and their functionality characterized using a strategy based upon the potential protein product predicted from flanking exon data. The functionality analyses suggest that four of the genes code for functional copies of calmodulin. All five copies have been identified across a wide range of littorinid species although not ubiquitously. Using this novel approach based on intron sequences, we have identified an unprecedented number of potential calmodulin copies in Littorina, exceeding that reported for any other invertebrate. This suggests a higher number of, and more ancient, gene duplications than previously detected in a single genus.

Calmyonemin: a 23 kDa analogue of algal centrin occurring in contractile myonemes of Eudiplodinium maggii (ciliate)

Myonemes are bundles of thin filaments (3-6 nm in diameter) which mediate calcium-induced contraction of the whole or only parts of the cell body in a number of protists. In Eudiplodinium maggii, a rumen ciliate which lacks a uniform ciliation of the cell body, myonemes converge toward the bases of apical ciliary zones that can be retracted under stress conditions, entailing immobilization of the cell. An mAB (A69) has been produced that identifies a calcium-binding protein by immunoblot, immunoprecipitation experiments and specifically labels the myonemes in immunoelectron microscopy. Solubility properties, apparent molecular weight (23 kDa) and isoelectric point (4.9) of the myonemal protein, are similar to the values reported for the calcium-modulated contractile protein centrin. Western-blot analysis indicates that the 23 kDa protein cross-reacts antigenically with anti-centrin antibodies. In addition, the 23 kDa protein displays calcium-induced changes in both electrophoretic and chromatographic behaviour, and contains calcium-binding domains that conform to the EF-hand structure, as known for centrin. Based on these observations, we conclude that a calcium-binding protein with major similarities to centrin occurs in the myonemes of E. maggii. We postulate that this protein plays an essential role in myoneme-mediated retraction of the ciliature.

Primary structure of a gene-sized DNA encoding calmodulin from the hypotrichous ciliate Stylonychia lemnae

We have isolated and characterized a gene-sized DNA encoding calmodulin (Clm) from macronuclear (MA) DNA of the hypotrichous ciliate, Stylonychia lemnae. The gene has 3500 copies per macronucleus. The length of the gene was deduced by agarose-gel electrophoresis of MA DNA and Southern blot analysis using a Clm cDNA probe from chicken. We then isolated the gene from a MA library. The overall length of the gene is 821 bp with a 450-bp intronless coding region. The deduced amino acid (aa) sequence of ciliate Clm has 149 aa and an M(r) of 16,819. Both ends of the cloned gene have the hypotrichous telomeric C4A4 repeat. The coding region is flanked by a 158-bp 5'-leader sequence and a 3'-trailer sequence of 213 bp. S1 analysis was used to locate the transcription start point (tsp) 49 bp upstream from the start codon. No common eukaryotic transcription signals were found upstream from the tsp. A second gene-sized DNA, detected by its cross-hybridization with the Clm DNA, predicts the existence of a second Ca(2+)-binding protein with only one Ca(2+)-binding site. It's function and biological significance is yet unknown.

Calmodulin cDNAs from two species of Tetrahymena

We describe the isolation and characterization of cDNAs encoding calmodulins of Tetrahymena thermophila and Tetrahymena pyriformis. It reveals that the deduced amino acid sequences of both calmodulins are precisely the same.

Study of the glycogenolytic action of platelet activating factor in Tetrahymena pyriformis

1. A novel action of AGEPC on non-inflammatory cells was revealed, namely the ability to stimulate glycogenolysis in Tetrahymena pyriformis cells. 2. The glycogenolytic effect of AGEPC seems to be dependent on Ca2+ transport and regulation, thus the effects are completely inhibited by Verapamil and partially by EGTA. 3. The influence of Propranolol, Labetalol, Atenolol and Theophylline in the glycogenolytic effect of AGEPC are also studied. 4. Our findings suggest that the AGEPC promoted glycogenolysis in Tetrahymena through a mechanism distinct from that of catecholamines.

Amino acid sequence of calmodulin from Euglena gracilis

The complete amino acid sequence of calmodulin from Euglena gracilis was determined by isolation and sequence analyses of peptides derived from calmodulin by digestion with trypsin and Staphylococcus aureus V8 protease. Euglena calmodulin consists of 148 amino acid residues; it lacks tryptophan and cysteine and contains one tyrosine, three histidine and two NE-trimethyllysine residues/molecule of the protein. Its N-terminus was blocked with an acetyl group and C-terminal lysine was trimethylated. Euglena calmodulin is the first calmodulin so far examined in which the C-terminal lysine is trimethylated. The comparison of amino acid sequences between Euglena and human brain calmodulins indicated 17 amino acid substitutions in Euglena calmodulin.

Isolation and purification of calmodulin from the shrimp, Crangon crangon

Calmodulin was isolated and purified from shrimp abdominal muscle by heat precipitation, ion exchange and hydrophobic interaction chromatography. The purified calmodulin was homogeneous when evaluated by polyacrylamide gel electrophoresis. A still remaining contaminant was eliminated by high performance liquid chromatography on a phenyl column. The biological and physicochemical properties of shrimp calmodulin such as amino acid composition, molecular weight and the ability to activate calmodulin-deficient bovine heart phosphodiesterase were compared to those of other invertebrate calmodulins.

The isolation and characterization of a calmodulin-encoding gene (CMD1) from the dimorphic fungus Candida albicans

Candida albicans is a dimorphic, opportunistic pathogen of humans, and calcium and calmodulin have been implicated in its morphogenic transition. The C. albicans calmodulin-encoding gene, CMD1, was isolated from cDNA and genomic phage lambda libraries using the Saccharomyces cerevisiae CMD gene as a hybridization probe. Southern-blot hybridization analysis of genomic DNA suggests the existence of only one type of calmodulin gene in C. albicans. Comparison of cDNA and genomic sequences identified a 222-bp intron located immediately after the Met start codon. The predicted amino acid sequence was 60% identical with yeast CMD and 70% identical with CMDs of filamentous fungi and vertebrates. We have localized the CMD1 gene to chromosome 3 using the contour-clamped homogeneous electric field gel electrophoresis. The CMD1 gene hybridized to a single 650-nucleotide transcript which was present in equivalent amounts in both the yeast and hyphal forms of the organism.

Analysis of the molecular basis of calmodulin defects that affect ion channel-mediated cellular responses: site-specific mutagenesis and microinjection

The ability of microinjected calmodulin to temporarily restore an ion channel-mediated behavioral phenotype of a calmodulin mutant in Paramecium tetraurelia (cam1) is dependent on the amino acid side chain that is present at residue 101, even when there is extensive variation in the rest of the amino acid sequence. Analysis of conservation of serine-101 in calmodulin suggests that the ability of calmodulin to regulate this ion channel-associated cell function may be a biological role of calmodulin that is widely distributed phylogenetically. A series of mutant calmodulins that differ only at residue-101 were produced by in vitro site-specific mutagenesis and expression in Escherichia coli, purified to chemical homogeneity, and tested for their ability to temporarily restore a wild-type behavioral phenotype to cam1 (pantophobiacA1) Paramecium. Calmodulins with glycine-101 or tyrosine-101 had minimal activity; calmodulins with phenylalanine-101 or alanine-101 had no detectable activity. However, as a standard of comparison, all of the calmodulins were able to activate a calmodulin-regulated enzyme, myosin light chain kinase, that is sensitive to point mutations elsewhere in the calmodulin molecule. Overall, these results support the hypothesis that the structural features of calmodulin required for the transduction of calcium signals varies with the particular pathway that is being regulated and provide insight into why inherited mutations of calmodulin at residue 101 are nonlethal and selective in their phenotypic effects.

Genes of Acanthamoeba: DNA, RNA and protein sequences (a review)

This review summarizes knowledge about the structure of nuclear genes and mitochondrial DNA in Acanthamoeba. The information about nuclear genes is derived from studies of DNA, RNA and protein sequences. The genes considered are those for 5S, 5.8S and 18S rRNA, actin I, profilins Ia/b and II, myosins IB, IC and II, and calmodulin. All of the sequences show strong similarities to comparable sequences from other organisms. Introns have been found in the actin and myosin genes. The location of the actin intron is unique, but many of the myosin introns occur at the same sites as introns in myosins of other organisms. Sequence comparisons, especially of 5S and 5.8S rRNA and actin, support previous evidence, based primarily on 18S rRNA, that Acanthamoeba genes are at least as closely related to those of higher plants and animals as they are to various other protistan genera. The functional organization of the promoter region for the nuclear rDNA transcription unit has been studied extensively, but there is a need for information about the functional organization of regulatory sequences for other genes. Restriction fragment length profile (RFLP) studies of mitochondrial DNA reveal relatively high levels of overall sequence diversity, but information on the structure and function of individual genes is needed. The RFLP appear to have potential as tools for taxonomic studies of this genus.

Evolution of EF-hand calcium-modulated proteins. I. Relationships based on amino acid sequences

The relationships among 153 EF-hand (calcium-modulated) proteins of known amino acid sequence were determined using the method of maximum parsimony. These proteins can be ordered into 12 distinct subfamilies--calmodulin, troponin C, essential light chain of myosin, regulatory light chain, sarcoplasmic calcium binding protein, calpain, aequorin, Stronglyocentrotus purpuratus ectodermal protein, calbindin 28 kd, parvalbumin, alpha-actinin, and S100/intestinal calcium-binding protein. Eight individual proteins--calcineurin B from Bos, troponin C from Astacus, calcium vector protein from Branchiostoma, caltractin from Chlamydomonas, cell-division-cycle 31 gene product from Saccharomyces, 10-kd calcium-binding protein from Tetrahymena, LPS1 eight-domain protein from Lytechinus, and calcium-binding protein from Streptomyces--are tentatively identified as unique; that is, each may be the sole representative of another subfamily. We present dendrograms showing the relationships among the subfamilies and uniques as well as dendrograms showing relationships within each subfamily. The EF-hand proteins have been characterized from a broad range of organismal sources, and they have an enormous range of function. This is reflected in the complexity of the dendrograms. At this time we urge caution in assigning a simple scheme of gene duplications to account for the evolution of the 600 EF-hand domains of known sequence.

Substitution at position 116 of Schizosaccharomyces pombe calmodulin decreases its stability under nitrogen starvation and results in a sporulation-deficient phenotype

We constructed Schizosaccharomyces pombe strains that carry phenylalanine, instead of arginine, as residue 116 of calmodulin by site-directed mutagenesis of the cam1 gene. Whereas haploid strains carrying the mutant allele, designated cam1-F116, exhibit no defects in growth and mating, diploid strains homozygous for cam1-F116 are deficient in sporulation. The four nuclei generated by the two serial meiotic divisions are not encapsulated in these diploids. The mutation is recessive. Semiquantitative analysis using polyclonal antibodies showed that vegetatively growing cam1-F116 cells have a smaller amount of calmodulin than wild-type cells. The quantitative difference becomes more remarkable if the cells are starved for nitrogen, which is a condition for induction of sporulation. In addition to this in vivo observation, we showed in vitro that the mutant protein is susceptible to a proteolytic activity induced by nitrogen starvation that hardly affects the wild-type calmodulin. Thus, the sporulation deficiency of the cam1-F116 mutant may be ascribed to shortage of calmodulin due to proteolysis of the mutant molecules under nitrogen starvation. Two other mutations at position 116 resulted in similar but leakier Spo- phenotypes.

Functional expression of chicken calmodulin in yeast

The coding region of a chicken calmodulin cDNA was fused to a galactose-inducible GAL1 promoter, and an expression system was constructed in the yeast Saccharomyces cerevisiae. Expression of calmodulin was demonstrated by purifying the heterologously expressed protein and analyzing its biochemical properties. When the expression plasmid was introduced into a calmodulin gene (cmd1)-disrupted strain of yeast, the cells grew in galactose medium, showing that chicken calmodulin could complement the lesion of yeast calmodulin functionally. Repression of chicken calmodulin in the (cmd1)-disrupted strain caused cell cycle arrest with a G2/M nucleus, as observed previously with a conditional-lethal mutant of yeast calmodulin. These results suggest that the essential function of calmodulin for cell proliferation is conserved in cells ranging from yeast to vertebrate cells.

Theoretical estimation of the calcium-binding constants for proteins from the troponin C superfamily based on a secondary structure prediction method. I. Estimation procedure

Proteins belonging to the TNC superfamily are known to be built of two, three, four, or six domains of closely similar amino acid sequences. Each domain binds no more than one calcium ion and shows a characteristic helix-loop-helix structure when in the calcium-bound state. Conformational properties of all the domains known so far have been analysed by us using a secondary structure prediction method (Garnier, J., Osguthorpe, D.J. & Robson, B. (1978). J. molec. Biol. 120, 97). Significant differences in distribution of residues predicted as being in the helical, beta-turn, and coil conformations have been found between the strongly, weakly, and non-binding domains. We could determine the ideal prediction pattern characteristic for the domains with the highest affinity for calcium. On the basis of our analysis and observations made by other authors we worked out a few simple rules which made it possible to compare conformational properties of a given domain with the ideal reference pattern and estimate, in this way, the Ca2+-binding constant of the domain. In native proteins the domains are known to be organized in pairs. The Ca2+-binding constant for a two-domain region could be evaluated from the sum of the estimation points attributed to each of its components. Using our method it is possible to predict the binding constants of typical domains and two-domain regins with a precision of one order of magnitude. Data on amino acid sequences and calcium-binding constants of all known proteins, believed to be the members of the TNC superfamily, have been reviewed. References to virtually all papers published on this subject before the end of 1987 are given.

Amino acid sequence of a calcium-binding protein (TCBP-10) from Tetrahymena

The amino acid sequence of a calcium-binding protein obtained from the cilium and cell body of Tetrahymena, designated as TCBP-10 (Tetrahymena calcium-binding protein; molecular mass = 10 kDa [Ohnishi, K. and Watanabe, Y. (1983) J. Biol. Chem. 258, 13978-13985] was determined. It is composed of 102 amino acid residues. The exact molecular mass is calculated to be 11563 Da. From the amino acid sequence analysis, it has two EF-hand-type calcium-binding sites.

Two calmodulin genes are expressed in Arbacia punctulata. An ancient gene duplication is indicated

Calmodulin is highly conserved, and only in the sea urchin Arbacia punctulata have two distinct isotypes been reported. We have isolated and sequenced two cDNAs from a lambda gt 11 library constructed from RNA from ovary tissue of A. punctulata. One clone, designated alpha, encodes a calmodulin isotype previously designated A. It encodes an amino acid sequence that is identical with calmodulin of most vertebrates in positions 1 through 141; however, it does not encode the last seven amino acids. The other clone, designated beta, starts with an open reading frame and encodes the B form of calmodulin from position 11 through the C-terminal position 148. It has only four differences from vertebrate calmodulin, occurring at positions 78 (Asp, beta Glu), 99 (Tyr, beta Phe), 143 (Gln, beta Ala) and 147 (Ala, beta Ser). The nucleic acid sequences of the alpha and beta cDNAs differ at 46 nucleotide positions that are distributed throughout their coding sequences. We conclude that the corresponding mRNAs are not derived from post-transcriptional processing of a single gene, and we infer that they are transcribed from two non-allelic genes. The gene duplication is inferred to have occurred prior to the divergence of the vertebrates and the echinoderms. The expression of these calmodulin mRNAs in ovary tissue and eggs of a single animal differs as judged by hybridization of probes to RNA immobilized to filters.

Purification and biochemical properties of calmodulin from Saccharomyces cerevisiae

Calmodulin from the yeast Saccharomyces cerevisiae was purified to complete homogeneity by hydrophobic interaction chromatography and HPLC gel filtration. The biochemical properties of the purified protein as calmodulin were examined under various criteria and its similarity and dissimilarity to other calmodulins have been described. Like other calmodulins, yeast calmodulin activated bovine phosphodiesterase and pea NAD kinase in a Ca2+-dependent manner, but its concentration for half-maximal activation was 8-10 times that of bovine calmodulin. The amino acid composition of yeast calmodulin was different from those of calmodulins from other lower eukaryotes in that it contained no tyrosine, but more leucine and had a high ratio of serine to threonine. Yeast calmodulin did not contain tryptophanyl or tyrosyl residues, so its ultraviolet spectrum reflected the absorbance of phenylalanyl residues, and had a molar absorption coefficient at 259 nm of 1900 M-1 cm-1. Ca2+ ions changed the secondary structure of yeast calmodulin, causing a 3% decrease in the alpha-helical content, unlike its effect on other calmodulins. Antibody against yeast calmodulin did not cross-react with bovine calmodulin, and antibody against bovine calmodulin did not cross-react with yeast calmodulin, presumably due to differences in the amino acid sequences of the antigenic sites. It is concluded that the molecular structure of yeast calmodulin differs from those of calmodulins from other sources, but that its Ca2+-dependent regulatory functions are highly conserved and essentially similar to those of calmodulins of higher eukaryotes.

Structure and sequence of the Drosophila melanogaster calmodulin gene

A series of phage clones overlapping the single calmodulin gene locus of Drosophila melanogaster has been isolated and the exons of the gene positioned and sequenced within these clones. A calmodulin cDNA clone of the electric eel was used to identify these clones and to position the two major protein-coding exons of the gene. cDNA clones for D. melanogaster calmodulin were then isolated, characterized and used to identify the remaining exons. The gene consists of four exons separated by three introns of 3400 to 4300 bases in length. Exon 1 consists of the 5' untranslated region and the initiator ATG; exon 2 encodes amino acid residues 1 to 58.3; exon 3 encodes residues 58.3 to 139.3; and exon 4 encodes residues 139.3 to 148 and the 3' untranslated region. From the sequence of the 3' untranslated region and the lengths of the cDNA clones, two or three polyadenylation sites are indicated. Sequences potentially involved in the control of transcription of the gene and splicing of the mRNA product have been identified. Comparison of the intron-exon structures of the D. melanogaster calmodulin gene, the chick calmodulin gene, and other genes of the troponin C superfamily reinforces previous hypotheses that these genes arose from a common progenitor and permits identification of four introns that were probably present in the progenitor gene structure. The D. melanogaster calmodulin gene contains three of these introns, and the chick gene contains all four. These gene comparisons also indicate that the region of these genes encoding Ca2+-binding loop 3 is highly variable in structure. The chick and D. melanogaster calmodulin genes differ in this region, the chick gene containing a fifth intron here that is absent from the D. melanogaster gene.

Biochemical characterization of a genetically altered calmodulin in Paramecium

Recent evidence proposes that the calcium-binding protein, calmodulin, plays a crucial role in the regulation or modulation of the calcium-dependent potassium conductance in Paramecium tetraurelia (Hinrichsen, R.D., Burgess-Cassler, A., Soltvedt, B.C., Hennessey, T. and Kung, C. (1986) Science 323, 503-506). We purified the calmodulins from both the wild type and pantophobiac A (a mutant lacking the above-mentioned conductance and whose phenotypic defect is traceable to its calmodulin) by hydrophobic interaction and immunoaffinity chromatographies, and examined them biochemically. In this paper we address the preliminary characterization of the two calmodulins and discuss the consequences of the genetic alteration. The differences described here are in their electrophoretic mobilities in polyacrylamide gel electrophoresis and in their binding characteristics to monoclonal antibodies raised against calmodulin from wild-type paramecia. Also, we present data which indicate a difference in the stimulation of the calmodulin-dependent enzyme bovine brain phosphodiesterase under certain conditions.

A mutant Paramecium with a defective calcium-dependent potassium conductance has an altered calmodulin: a nonlethal selective alteration in calmodulin regulation

The Paramecium mutant, pantophobiac A, has a defect that results in an in vivo loss of calcium-dependent potassium efflux channel activity. This defect is corrected fully by the microinjection of wild-type Paramecium calmodulin into pantophobiac A cells and is partially restored by calmodulins from other organisms, but it cannot be restored by microinjection of pantophobiac calmodulin. Overall, these results suggested that wild-type Paramecium calmodulin has unique features that allow it to restore fully a normal phenotype and that the defect in pantophobiac A might be an altered calmodulin molecule. Previous studies established the amino acid sequence of wild-type calmodulin and showed that Paramecium calmodulin has several differences from other calmodulins, including the presence of dimethyllysine at residue 13. To test directly the possibility that calmodulin from the pantophobiac mutant might be altered, we purified the mutant calmodulin and compared its properties to those of wild-type Paramecium calmodulin. We found one amino acid sequence difference between the two Paramecium calmodulins: a phenylalanine in the mutant protein, instead of a serine, at residue 101. This change is at a calcium-liganding residue in the third calcium-binding loop. These and previous studies demonstrate that comparatively subtle changes in the structure of calmodulin can result in quantitative alterations in in vivo activity, provide insight into the in vivo roles of calmodulin and the regulation of ion channels, and demonstrate that functional alterations of calmodulin are not necessarily lethal.

Analysis and in vivo disruption of the gene coding for calmodulin in Schizosaccharomyces pombe

Calmodulin is a low molecular weight calcium-binding protein that modulates many enzyme systems in eukaryotes. We have cloned the gene encoding calmodulin from the fission yeast, Schizosaccharomyces pombe, by using synthetic oligonucleotide probes that correspond to three distinct regions of Tetrahymena calmodulin. A 1.6-kilobase (kb) DNA fragment that hybridized to all of them contains a gene whose deduced product possesses 74% amino acid homology with bovine calmodulin. This gene, which is unique in the S. pombe genome and is named cam1, encodes 149 amino acids excluding the first methionine and is transcribed into mRNA of 1.2-kb length. It has an intron that apparently starts immediately after the initiation codon and is 126 bp long. S. pombe calmodulin exhibits more homology to vertebrate calmodulin than to that of the budding yeast, Saccharomyces cerevisiae. Gene disruption experiments revealed that cam1 gene function is essential for vegetative growth of S. pombe. Spores bearing disrupted cam1 halt growth soon after germination and rarely carry out the first cell division, indicating that calmodulin does not exist in excess in those cells.

Possible origin of a calmodulin gene that lacks intervening sequences

The divergent, muscle-specific allele of the chicken calmodulin gene contains no intervening sequences and apparently was produced by a reverse transcriptase-mediated event. The nucleotide and deduced amino acid sequences of this gene were compared with nucleotide and amino acid sequence data of other known calmodulin genes in order to investigate its evolutionary history. These comparisons, as well as the CpG dinucleotide content, support the conclusion that this highly divergent chicken calmodulin gene did not exist for any significant period of times as a pseudogene and suggest plausible alternative genetic histories. The most parsimonious history involves the viral import of a very old foreign gene of high CpG content.

Structure of a gene for rat calmodulin

The structural organization of the entire rat calmodulin gene was determined by cloning and sequencing overlapping genomic and cDNA clones from rat genomic and brain cDNA libraries. The intron/exon organization was determined by direct comparison of these sequences. Rat calmodulin gene is 9000 bases long and consisted of six exons interrupted by introns of variable sizes. The first intron separates the initiation codon (ATG) from the coding region of the protein. Three out of four intron/exon junctions in the coding region reside in the middle of calcium binding subdomains and do not correlate with the quarterly divided intramolecular homology of the protein. Their positions exactly coincide with those of the corrected version of chicken calmodulin gene. The rat calmodulin gene harbors a stretch of sequences homologous to a rat middle repetitive "identifier sequence" in the middle of the third intron. Analysis of the immediate 5' upstream region detected a TATA box (TATATATAT) and three C-G boxes (CCGCCC) but not a CAT box (CCAAT). A conserved sequence (GCGCCGCGYCYYGGGGGC) was found at -125 for rat and at -204 for chicken calmodulin genes.

Properties of digitonin-solubilized calmodulin-dependent guanylate cyclase from the plasma membranes of Tetrahymena pyriformis NT-1 cells

Calmodulin-dependent guanylate cyclase from Tetrahymena plasma membranes was solubilized in about a 22% yield by using digitonin in the presence of 0.2 mM CaCl2 and 20% glycerol. The detergent, when present in the assay at concentrations above 0.05%, diminished the basal and calmodulin-stimulated activity of the enzyme. Guanylate cyclase solubilized with digitonin was eluted from DEAE-cellulose with 200 mM KCl in a yield of 50%. Properties of the solubilized enzyme were similar to those of the native membrane-bound enzyme. The Kms for Mg-GTP and Mn-GTP were 140 and 30 microM, respectively. The enzyme required Mn2+ for maximum activity, the relative activity in the presence of Mg2+ being 30% of the activity with Mn2+. The solubilized enzyme retained the ability to be activated by calmodulin, with its extent being reduced as compared to the membrane-bound enzyme. The presence of a Ca2+-dependent calmodulin-binding site on the solubilized enzyme was shown by the Ca2+-dependent retention of the enzyme on a calmodulin-Sepharose-4B column.

Isolation of the yeast calmodulin gene: calmodulin is an essential protein

Calmodulin was purified from Saccharomyces cerevisiae based on its characteristic properties. Like other calmodulins, the yeast protein is small, heat-stable, acidic, retained by hydrophobic matrices in a Ca2+-dependent manner, exhibits a pronounced Ca2+-induced shift in electrophoretic mobility, and binds 45Ca2+. Using synthetic oligonucleotide probes designed from the sequences of two tryptic peptides derived from the purified protein, the gene encoding yeast calmodulin was isolated. The gene (designated CMD1) is a unique, single-copy locus, contains no introns, and resides on chromosome II. The amino acid sequence of yeast calmodulin shares 60% identity with other calmodulins. Disruption or deletion of the yeast calmodulin gene results in a recessive-lethal mutation; thus, calmodulin is essential for the growth of yeast cells.

Structure of rat calmodulin processed genes with implications for a mRNA-mediated process of insertion

Two distinct processed calmodulin genes of rat (lambda SC8 and lambda SC9) were identified, cloned and their DNA sequences determined. The existence of direct repeats of 19 base-pairs for lambda SC8 or 9 base-pairs for lambda SC9 at both ends of the coding plus non-coding regions suggested a possible involvement of a mRNA-mediated process of insertion. Total genomic Southern hybridization suggested the existence of at least three different calmodulin-related genes in the rat genome. The other gene was the bona fide calmodulin gene (lambda SC4) which was split into at least five exons. lambda SC9 contained insertions of one nucleotide and two 17 base-pair direct repeats in the coding region. These insertions cause frameshift mutations probably preventing it from encoding a functional calmodulin. It also carried an insertion of a rat middle repetitive sequence, identifier sequence (IDS: Sutcliffe et al., 1982) in the 3'-non-coding region. Otherwise, it consisted of an almost identical DNA sequence to that of the bona fide calmodulin gene (lambda SC4), including the 3'-non-coding region down to the poly(A) recognition signal, A-A-T-A-A-A. On the other hand, lambda SC8 did not possess frameshift mutations in the coding region, and hence was capable of encoding a functional protein. In fact, a probe specific to the lambda SC8 sequence identified a band in Northern blotting whose size was 300 nucleotides smaller than that of authentic calmodulin mRNA. Comparison of the nucleotide sequences showed that only the coding regions of these two processed genes were homologous, indicating that the divergence of these two processed genes from the common ancestor calmodulin was an ancient event.

A novel calmodulin-like gene from the nematode Caenorhabditis elegans

A novel gene from the nematode Caenorhabditis elegans was isolated by hybridization with a human calmodulin complementary DNA probe. This gene, cal-1, is present at one copy per haploid genome. In-situ hybridization of the cloned gene to metaphase chromosomes allowed us to assign it to the nematode linkage group IV. The polypeptide predicted from the sequence of this gene displays structural features of both calmodulin and troponin C.

Yeast gene required for spindle pole body duplication: homology of its product with Ca2+-binding proteins

Saccharomyces cerevisiae strains bearing temperature-sensitive alleles of the cell division cycle gene CDC31 are specifically defective in duplication of the spindle pole body, the microtubule-organizing center of yeast. To define the function encoded by CDC31 more fully, we have isolated genomic clones of the gene by selection for complementation of a temperature-sensitive allele. The locus from which the clone was derived was marked by integration of a nutritional marker and found by meiotic mapping to cosegregate with CDC31. The polypeptide sequence of the open reading frame in the CDC31 gene was determined and compared with the sequences of other known proteins. This revealed significant homology with the calmodulins and other members of the Ca2+-binding protein family. On the basis of comparison with these related proteins, it is evident that the CDC31 gene product has at least two binding sites for Ca2+ and is also homologous with other regions of the calmodulin sequence. We propose that Ca2+ fluxes within the yeast cell play a key role in spindle pole body duplication and consequently in the organization of the microtubule arrays.

Two calmodulins in Naegleria flagellates: characterization, intracellular segregation, and programmed regulation of mRNA abundance during differentiation

Flagellates of Naegleria gruberi contain two calmodulins that differ in apparent molecular weight and intracellular location. Calmodulin-1, localized in flagella, has an apparent molecular weight of approximately 16,000, approximately the size of other protozoan calmodulins, whereas calmodulin-2, localized in cell bodies, is 15,300. Both proteins, purified, are calmodulins by several criteria, including Ca2+-dependent stimulation of calmodulin-dependent cyclic nucleotide phosphodiesterase and affinity for antibodies to vertebrate calmodulin. The finding of two calmodulins is unusual. Since the only known difference is apparent molecular weight, one calmodulin could be derived from the other, except that both calmodulins are synthesized in a wheat germ, cell-free system directed by RNA from differentiating Naegleria. Translatable mRNAs encoding calmodulins 1 and 2, not detected in amebas, appear and subsequently disappear concurrently during the 100-min differentiation of Naegleria from amebas to flagellates. Furthermore, these mRNAs increase and then decrease in abundance concurrently with those for flagellar tubulins, which suggests the possibility that the expression of the unrelated genes for calmodulin and tubulin may be under coordinate control during differentiation.