Characteristics of the translation of thymosin alpha 1 precursor mRNA by cell-free wheat germ system. Evidence for the acetylation of thymosin alpha 1 precursor

At the optimal concentrations of Mg2+ and K+ to translate total thymus PolyA+-RNA, the purified thymosin alpha 1 precursor mRNA saturate the protein synthetic activity at lower concentration than the total thymus mRNAs. The polyamine spermidine increases the translation rate of the messenger, which is modulated by magnesium, rather than improve the yield in full-length chains of thymosin alpha 1 precursor. As other eukariotic mRNAs, this messenger presents the "cap" modification at the 5'-end terminal position. The incorporation of [3H]acetate into the translation product of the messenger, shows an evidence for the acetylation of the thymosin alpha 1 precursor during its biosynthesis in vitro.     

Separation of rosette formation-inducing polypeptides from the supernatant of cultures of rat thymic epithelial cell line

Four polypeptide fractions were isolated by high-pressure liquid chromatography (HPLC) from culture supernatant of rat thymic epithelial cell line (IT-45R1). Biological activity of these fractions was examined according to the capacity inducing rosette-formation between rat thymocytes and guinea pig erythrocytes. A relatively rich population of non-rosette-forming cells (non-RFC), one of targets for thymic hormones, was separated from rat thymocytes by combining rosette-formation method with differential centrifugation. Non-RFC consists of outer-cortical and medullary thymocytes. Medullary thymocytes treated with the polypeptide fraction did not differentiate into RFC. Therefore, the cells, which rosette-forming capacity was induced, seem to derive from outer-cortical area. One of the polypeptide fractions (estimated molecular weight: 3 K) possessed the activity endowing non-RFC with rosette-forming capacity. Since its molecular weight was similar to that of thymosin alpha 1, the fraction was pretreated with anti-thymosin alpha 1 antiserum. The pretreatment suppressed the activity of the fraction. Thus, the fraction must contain thymosin alpha 1 or a polypeptide possessing an antigenic determinant similar to that of thymosin alpha 1. Moreover, two of four subfractions, which were divided from the active fractions by reversed-phase HPLC, showed the biological activity.     

Translation of mRNA for glutamate dehydrogenase and spectrophotometric procedure to follow the enzyme biosynthesis.

Heterogeneous poly (A)-mRNA fraction was isolated from rat liver microsomes using phenol-chloroform extraction, millipore filtration and poly (U)-agarose affinity chromatography. Obtained fractions were characterized with respect to their secondary structure and poly (A) content. Isolated poly (A)-mRNA fraction contained high template activity for glutamate dehydrogenase in cell-free systems with microsomes or polysomes. A spectrophotometric procedure to follow enzyme biosynthesis was also developed.     

Isolation and identification of thymosin alpha 1 from calf spleen using high performance liquid chromatography

A peptide isolated from calf spleen has been identified as thymosin alpha 1. The isolation involved defatting of the desiccated glands with acetone, extraction of the acetone power with pyridine acetate pH 5.5, heat denaturation, reverse phase chromatography on an RP-8 column, anion exchange chromatography on a Partisil SAX column and, finally, reverse phase purification on a microBondapak C18 column. The identification was based on: 1) amino acid analysis; 2) thermolysin digest; and 3) retention time in two different HPLC systems. The amount isolated from the spleen was 10-20% of that isolated from calf thymus glands.     

Evidence for the synthesis of thymosin alpha 1 by calf thymocytes and the production of this peptide by natural processing

Thymus and thymocytes from calf were extracted under isotonic conditions in the presence of protease inhibitors or under severe denaturing conditions (after quick freezing and thawing in boiling 0.1 M NaCl). The extracts, as well as the medium in which the thymocytes were obtained from thymus fragments (thymocyte supernatants), were size-fractionated by ultrafiltration. As in whole thymus isotonic extracts, thymosin alpha 1 [A. L. Goldstein, T. L. K. Low, M. McAdoo, J. McClure, G. B. Thurman, J. Rossio, C-Y. Lai, D. Chang, S-S. Wang, C. Harvey, A. H. Ramel, and J. Meienhofer (1977) Proc. Natl. Acad. Sci. USA 74, 725-729] was contained in isotonic extracts from thymocytes and also in thymocyte supernatants, as determined by isoelectric focusing and reverse-phase HPLC analysis. The extraction under denaturing conditions mainly yielded products with molecular masses over 50,000, showing very similar isoelectric focusing patterns in both thymocytes and whole thymus extracts. As deduced by isoelectric focusing analysis of diverse size-fractionated products, a strong association capacity seems to be responsible for an apparently high molecular mass of the components of these extracts. According to the pI, two of these components were prothymosin alpha [A. A. Haritos, G. J. Goodall, and B. L. Horecker (1984) Proc. Natl. Acad. Sci. USA 81, 1008-1011] and thymosin alpha 1. Prothymosin alpha was not detected in any isotonic extracts or thymocyte supernatants. These data suggest that calf thymocytes are capable of producing thymosin alpha 1, which would arise by natural processing of its precursor.     

Solid-phase synthesis of biologically active fragment 29-111 of rat prothymosin alpha

Rat prothymosin alpha fragment 29-111, an 83-residue polypeptide corresponding to desthymosin alpha 1-prothymosin alpha, has been synthesized by a solid-phase method. Hydrogen fluoride was used to deprotect and cleave the peptide from the resin. The crude product was purified by gel-filtration, ion-exchange chromatography and high-performance liquid chromatography. A 3.2-mg sample of a ca. 96% pure peptide was finally obtained. The overall yield of the synthesis was less than 1%. An increase of E-rosette-forming lymphocytes was obtained after incubation of peripheral blood from uremic patients with the synthetic prothymosin alpha fragment 29-111. The restoring effect of the synthetic prothymosin alpha fragment 29-111 was greater than that of our synthetic thymosin alpha 1.     

Comparison of the crystallin mRNA populations from rat, calf and duck lens. Evidence for a longer alpha A2-mRNA and two distinct alpha B2-mRNAs in the birds

Total cytoplasmic poly(A)-containing RNA from rat, calf and duck lens was fractionated by electrophoresis in methylmercury hydroxide-containing agarose gels. RNA electrophoresed in parallel lanes was either transferred onto nitrocellulose and hybridized with total cDNA synthesized on the initial mRNA or was recovered from individual gel fractions for in vitro translation in a reticulocyte cell-free system. This allowed the identification and size-characterization of individual mRNA species encoding alpha-, beta-, gamma- and delta-crystallin polypeptides. The 14 S mRNA fraction of rat lens comprises two alpha A2-mRNAs of approximately 1250 and 1350 nucleotides and the alpha AIns-mRNA with a size similar to that of the largest alpha A2-mRNA. The calf lens 14 S mRNA fraction harbors a heterogeneous population of alpha A2-mRNA. In the same fraction another mRNA encoding a polypeptide, designated X, has been found sharing no homology with alpha A sequences. The duck lens alpha A2-mRNA appears to be 400-450 bases longer than the rat and calf lens alpha A2-mRNAs. Furthermore, in contrast to the single alpha B2-mRNA in rat and calf lens, two alpha B2-mRNAs have been identified in duck lens, one, the major species, similar in size to the alpha B2-mRNA in rat and calf lens (800 bases), and the other species 700 nucleotides longer. The large size differences among the alpha A2- and alpha B2-mRNAs most likely reside in their 3'-untranslated sequences.     

Biotechnological production of acetylated thymosin beta4

Thymosin beta4 (43 aa) is a highly conserved acidic peptide which regulates actin polymerization in mammalian cells by sequestering globular actin. Thymosin beta4 is undergoing clinical trials as a drug for the treatment of venous stasis ulcers, corneal wounds and injuries, as well as acute myocardial infarction. Currently, thymosin beta4 is produced with solid-phase chemical synthesis. Biotechnological synthesis of this peptide presents difficulties because N-terminal amino acid residue of thymosin beta4 is acetylated. In this study we propose a method for producing the recombinant precursor of thymosin beta4 and its subsequent targeted chemical acetylation. Desacetylthymosin beta4 was synthesized as a part of a hybrid protein with thioredoxin and a specific TEV (tobacco etch virus) protease cleavage site. The following scheme was developed for the purification of desacetylthymosin beta4: (i) the biosynthesis of a soluble hybrid protein (HP) in Escherichia coli; (ii) isolation of the HP by ion exchange chromatography; (iii) cleavage of the HP with TEVprotease; (iv) purification of desacetylthymosin beta4 by ultra-filtration. N-terminal acetylation of desacetylthymosin beta4 was performed with acetic anhydride under acidic conditions (pH 3). The reaction yield was 55%. Thymosin beta4 was then purified by reverse-phase high performance liquid chromatography. The proposed synthetic approach to recombinant thymosin beta4 is suitable for scale-up and can provide for the medical use of highly purified preparation with a yield of 20 mg from 1 L of culture.     

Purification of the secretor-type beta-galactoside alpha 1----2-fucosyltransferase from human serum.

The secretor-type beta-galactoside alpha 1----2-fucosyltransferase from human serum was purified by hydrophobic chromatography on phenyl-Sepharose, ion-exchange chromatography on sulfopropyl-Sepharose, and affinity chromatography on GDP-hexanolamine-Sepharose. Final purification of the enzyme was achieved by high pressure liquid chromatography gel filtration and resulted in a homogeneous protein as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the radiolabeled protein. The native enzyme appears as a molecule of apparent Mr 150,000 as determined by gel filtration high pressure liquid chromatography. The apparent Mr of the enzyme resolved in the presence of beta-mercaptoethanol by sodium dodecyl sulfate-polyacrylamide gel electrophoresis was determined to be 50,000, indicating a multisubunit structure of the enzyme. Secretor-type alpha 1----2-fucosyltransferase is a glycoprotein as determined by WGA binding properties. A comparison of the Mr of the native blood group H gene encoded with the secretor-type beta-galactoside alpha 1----2-fucosyltransferases as well as comparison of subunit Mr for both enzymes suggests structural similarity. The alpha 1----2 linkage formed between alpha-L-fucose and terminal beta-D-galactose by the purified H- and secretor-type alpha 1----2-fucosyltransferases was determined by 1H NMR homonuclear cross-irradiation analysis of the oligosaccharide products. The substrate specificity and Km values calculated from the initial rate using various oligosaccharide acceptors showed that purified enzymes differ primarily in affinity for phenyl-beta-D-galactopyranoside and GDP-fucose as well as type 1 (Gal beta 1----3GlcNAc), 2 (Gal beta 1----4GlcNAc), and 3 (Gal beta 1----3GalNAc) oligosaccharide acceptors. The secretor-type alpha 1----2-fucosyltransferase shows significantly lower affinity than the H enzyme for phenyl-beta-D-galactopyranoside and GDP-fucose as well as for type 2 oligosaccharide acceptors. On the contrary, type 1 and 3 oligosaccharide acceptors are preferentially utilized by the secretor-type enzyme as compared with the H enzyme. The enzymes also differ in several physicochemical properties, implying nonidentity of the two enzymes (Sarnesto, A., K?hlin, T., Thurin, J., and Blaszczyk-Thurin, M. (1990) J. Biol. Chem. 265, 15067-15075).     

Isolation of alpha 6 beta 1 integrins from platelets and adherent cells by affinity chromatography on mouse laminin fragment E8 and human laminin pepsin fragment

Ligand affinity chromatography was used to identify receptors on platelets and two adherent cell lines, OV-CAR-4 and HBL-100, for the E8 fragment of murine laminin. A complex of two polypeptides (140 and 110 kDa nonreduced) was bound by the E8 affinity columns from all three cell types and was eluted with EDTA. This heterodimeric complex was identified as the alpha 6 beta 1 integrin by immunoprecipitation with specific antibodies against either the alpha 6 or the beta 1 subunit. The alpha 6 beta 1 integrin did not bind to an affinity column containing fragment P1 originating from a different part of murine laminin which, however, bound the alpha IIb beta 3 integrin from platelets. Furthermore, in immunofluorescence staining, the alpha 6 beta 1 integrin localizes in focal contacts of OVCAR-4 cells attached to laminin and E8 but not to fibronectin substrates. These results, combined with previous antibody inhibition studies, unequivocally identify the alpha 6 beta 1 integrin as a specific receptor for fragment E8. Affinity chromatography of OVCAR-4 and HBL-100 cells on a large pepsin fragment of laminin from human placenta yielded integrin alpha 3 beta 1. When alpha 3 beta 1 was removed from lysates of OVCAR-4 cells by preclearing with an alpha 3-specific monoclonal antibody, alpha 6 beta 1 was able to bind to human laminin as well. Integrin alpha 6 beta 1 on platelets which do not express alpha 3 beta 1 binds directly to human laminin. These results indicate that both alpha 3 beta 1 and alpha 6 beta 1 can act as receptors for human laminin and may interfere by steric hindrance. The alpha 6 beta 4 complex, which is strongly expressed on HBL-100 cells, did not bind to either mouse laminin fragment E8 or human laminin affinity columns.     

Nuclear targeting of prothymosin alpha

Prothymosin alpha is a highly acidic protein which lacks an amino-terminal signal peptide, yet was once thought to be a precursor for thymosin alpha 1, a putative peptide hormone secreted by the thymus. Here, two lines of evidence are presented that strongly implicate prothymosin alpha as a nuclear protein: 1) in COS cells transfected with the human prothymosin alpha gene copious amounts of prothymosin alpha were present in sealed nuclei obtained by treating these cells with cytochalasin B and enucleating them centrifugally. 2) Constructs in which human prothymosin alpha nucleic acid sequences were fused in-frame either near the amino terminus of the beta-galactosidase gene in pCH110 or at the carboxyl terminus, when expressed in COS cells, resulted in nuclear localization of the fusion protein; indirect immunofluorescence in situ was used as the assay. The basic cluster of amino acids at the carboxyl terminus of prothymosin alpha, TKKQKT, has been identified as part of the nuclear targeting signal, whereas the basic cluster of amino acids situated within the thymosin alpha 1 sequence at the amino terminus failed to effect nuclear transport.     

Galpha(i2)-mRNA and -protein regulation as a mechanism for heterologous sensitization and desensitization of insulin secretion

Prolonged exposure of cells to an agonist of a G-protein-coupled receptor usually results in an attenuation of the cellular response. To elucidate the cellular mechanisms of sensitization or desensitization in an insulin secretory cell system (INS-1 cells), we investigated a regulatory link between G-protein alpha(s)- and alpha(i2)-subunits mRNA, their protein levels and insulin secretion as the biological effect using various compounds. Incubation with epinephrine (50 microM) for 8 h decreased alpha(s)- and alpha(i2)-mRNA levels to 58% and 72%, respectively, which is reversed after a longer incubation. From results using isoprenaline and the alpha2-agonist UK 14,304 epinephrine is shown to mediate its actions via alpha2- but not beta-adrenoceptors. The insulin inhibitory neuropeptide galanin (50 nM) caused a decrease of alpha(s)- and alpha(i2)-mRNA levels, whereas insulinotropic compounds (incretin hormones) such as GIP or GLP-1 (both 10 nM) led to an increase of alpha(s)- and alpha(i2)-mRNA levels. By using the Ca2+ channel blocker verapamil (50 microM) alpha(i2)-mRNA changes clearly depend on Ca2+ influx. The effects on alpha(i2)-mRNA were accompanied by a parallel, albeit weaker effect on the protein level (only GIP and UK 14,304 were investigated). The changes in alpha(i2)-mRNA levels by either compound were paralleled by inverse changes in insulin secretion: preincubation with UK 14,304 for 8 h led to an increased insulin secretion when challenged by either GLP-1, GIP or glucose (8.3 mM). This was similar for galanin, another potent inhibitor of insulin release. On the other hand, exposure to the incretins GIP or GLP-1 for 8 h induced a smaller insulin release when challenged afterwards by either UK 14,304, galanin, GIP, GLP-1, or glucose. Thus the influence on insulin secretion of various compounds is reciprocal to the regulation of alpha(i2)-mRNA levels but not alpha(s)-mRNA levels. There is, therefore, evidence from all the manoeuvres used that alpha(i2)-mRNA regulation may play a role in heterologous sensitization and desensitization of insulin secretion.     

Overexpression of soluble human thymosin alpha 1 in Escherichia coli

Synthesized gene of human thymosin alpha 1 (Tα1) was inserted into pET-28a, pET-9c,pThioHis B, pGEX-2T or pBV222 and then inductively expressed in strains of Escherichia coll. Among the five expression systems, the BL21/pET-28a system provides the highest expression level of fusion protein in a soluble form, which is up to 70% of total expressed bacterial proteins as visualized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The resulting fusion protein purified through nickel affinity chromatography accounts for 2.53% of the wet bacterial pellet weight and reaches 94.5% purity by SDS-PAGE. These results indicate the potential of this expression system for high-throughput production of recombinant Tα1.     

Isolation of rat serum alpha 1-microglobulin. Identification of a complex with alpha 1-inhibitor-3, a rat alpha 2-macroglobulin homologue.

Alpha 1-Microglobulin (alpha 1-m), or protein HC, a low molecular weight plasma protein with immunoregulatory properties, was isolated from rat serum by affinity chromatography using Sepharose-coupled monoclonal anti-alpha 1-m antibodies. High molecular weight forms of alpha 1-m were then separated from the low molecular weight alpha 1-m by gel chromatography of the eluted proteins. The apparent Mr (28,000), the charge heterogeneity, the N-linked carbohydrate, and yellow-brown chromophore suggest that the low molecular weight alpha 1-m is the serum counterpart to urinary alpha 1-m, which was purified previously. A high molecular weight complex of alpha 1-m was also isolated by the gel chromatography. It was homogeneous as judged by nondenaturing polyacrylamide gel electrophoresis. The molecule was bound by antibodies against human alpha 2-macroglobulin, and experiments with antisera against the three alpha-macroglobulin variants in rat serum, alpha 1-macroglobulin, alpha 2-macroglobulin, and alpha 1-inhibitor-3 (alpha 1I3) suggested that alpha 1I3 was the complex-partner of alpha 1-m. An antiserum raised against high molecular weight alpha 1-m was then used to isolate the complex-partner of alpha 1-m from rat serum with affinity chromatography, and this molecule was positively identified as alpha 1I3 by its physicochemical properties. Gel chromatography of the alpha 1I3.alpha 1-m complex suggested a molecule with an Mr of 266,000. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, however, it migrated as three major molecular species with apparent molecular weights of 224,000, 205,000, and 194,000 and several minor species of both higher and lower molecular weights, suggesting a complex subunit structure. alpha 1-m and alpha 1I3 could be detected in all three major species by Western blotting, and NH2-terminal amino acid sequencing suggested a molar ratio of 1:1 of alpha 1-m and alpha 1I3 in all three species. alpha 1I3.alpha 1-m was colorless, did not show light absorbance beyond 300 nm which is typical of low molecular weight alpha 1-m and was electrophoretically homogeneous, suggesting that it lacks the chromophore. Finally, the serum concentrations of the alpha 1I3.alpha 1-m complex and free alpha 1-m were determined as 0.16 and 0.010 g/liter, respectively. Thus, alpha 1I3.alpha 1-m constitutes 1-3% of the total alpha 1I3 in rat serum (w/w) and approximately 60% of the total alpha 1-m.     

Functional integrins from normal and glycosylation-deficient baby hamster kidney cells. Terminal processing of asparagine-linked oligosaccharides is not correlated with fibronectin-binding activity.

We have examined the properties of the alpha 5 beta 1 integrin of baby hamster kidney (BHK) cells, a ricin-resistant variant Ric14 lacking N-acetylglucosaminyl transferase I, and hence unable to complete assembly of hybrid- or complex-type N-glycans, and BHK cells treated with 1-deoxymannojirimycin (dMM), an inhibitor of Golgi mannosidases involved in the initial processing of N-glycan precursors. Comparable amounts of alpha 5 beta 1 integrin were isolated from these cells by chromatography of detergent extracts on a fibronectin cell-binding fragment affinity column and elution with EDTA. The alpha 5 beta 1 integrin obtained from normal BHK cells by fibronectin affinity chromatography contained mainly endoglycosidase H-resistant oligosaccharides, whereas in RicR14 cells or dMM-treated BHK cells these were entirely endoglycosidase H-sensitive. Analysis of lactoperoxidase labeled or long term biosynthetically 35S-labeled proteins from cultures of normal or glycosylation deficient cells showed similar steady state levels of alpha 5 beta 1 integrin and expression at the cell surface. Pulse-chase experiments in normal BHK cells showed rapid conversion of the alpha 5 subunit into a mature form containing oligosaccharides resistant to endoglycosidase H and slower maturation of a precursor beta 1 subunit, as in other cell types. In Ric14 cells the precursor beta 1 subunit was found to carry glycans larger than the fully processed Man5GlcNAc2 glycan of the mature subunit, indicating that the bulk precursor pool had not been translocated into the cis-Golgi compartment containing mannosidase I. We conclude that in BHK cells terminal oligosaccharide processing of alpha 5 beta 1 integrin subunits is not required for dimer formation, surface expression, and fibronectin binding, and that expression of the glycosylation defect of Ric14 cells on the alpha 5 beta 1 integrin does not account for the reduced adhesiveness of these cells on fibronectin compared with normal and dMM-treated BHK cells.     

重组胸腺素α1的表达、纯化和生物学活性

为获得重组人胸腺素α1(recombinantthymosinα1,Tα1) ,采用融合表达方式表达Tα1基因 ,重组融合表达载体Tα1 pGEX 4XT 1转化大肠杆菌DE3(lys)构建工程菌 .对工程菌进行补料分批培养并诱导表达 ,得到目的蛋白的可溶性表达 .亲和层析纯化融合蛋白GST Tα1,经凝血酶裂解融合蛋白 ,亲和层析除去GST ,SourceQ离子交换 ,得到Tα1单体 ,得率为 30mg L发酵液 .生物学活性分析显示 ,重组Tα1能显著促进小鼠脾细胞增殖 (P <0 0 1) ,其活性与天然Tα1相似     

Purification of the beta-N-acetylglucosaminide alpha 1----3-fucosyltransferase from human serum.

A beta-N-Acetylglucosaminide alpha 1----3-fucosyltransferase was purified from human serum by ammonium sulfate precipitation, hydrophobic chromatography on phenyl-Sepharose, ion-exchange chromatography on sulfopropyl-Sepharose, affinity chromatography on GDP-hexanolamine-Sepharose, and finally high pressure liquid chromatography gel filtration. Gel filtration chromatography of the native enzyme revealed a Mr of 45,000. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the purified protein also appeared as a single molecular species of Mr 45,000. In contrast to the multisubunit beta-galactoside alpha 1----2-fucosyltransferases with an apparent Mr of 150,000, present in human serum, the native beta-N-acetylglucosaminide alpha 1----3-fucosyltransferase is a monomer with a Mr of 45,000. The enzyme is glycosylated, as revealed by wheat germ agglutinin binding properties. The alpha 1----3 linkage formed by the enzyme between alpha-L-fucose and the penultimate beta-N-acetylglucosamine by the purified enzyme was confirmed by 1H NMR homonuclear cross-irradiation analysis of the oligosaccharide product. The specificity of the purified enzyme is restricted to type 2 structures, as revealed by its reactivity with different substrates and from the Km values calculated from the initial rate data using various oligosaccharide acceptors. The enzyme has the ability to utilize the N-acetyl-beta-lactosamine determinant (Gal beta 1----4GlcNAc) and the sialylated (NeuAc alpha 2----3Gal beta 1----4GlcNAc) and fucosylated (Fuc alpha 1----2Gal beta 1----4GlcNAc) derivatives of N-acetyl-beta-lactosamine and thus is distinct from both the human Lewis gene-encoded enzyme and the alpha 1----3-fucosyltransferase of the myeloid cell type.     

Thymosin alpha 1-like peptides: localization and biochemical characterization in the rat brain and pituitary gland

Using a radioimmunoassay for thymosin alpha 1, endogenous thymosin-like peptides were characterized in the rat brain and pituitary gland. Thymosin alpha 1-like peptides were present in high concentrations in hypothalamus and pituitary extracts. These peptides were characterized using gel filtration techniques and the main peak of immunoreactive thymosin had a molecular weight similar to that of thymosin alpha 1 (3108 daltons). Using HPLC techniques, one main peak of immunoreactivity was present in brain extracts, whereas two peaks were present in pituitary extracts, one of which coeluted with thymosin alpha 1. The discrete regional distribution of thymosin alpha 1-like peptides was investigated and the highest densities of immunoreactive thymosin were present in the median eminence and arcuate nucleus of the hypothalamus, as well as the neurointermediate lobe of the pituitary. Due to the anatomical proximity of immunoreactive thymosin to loci containing known releasing factors and hormones, thymosin alpha 1-like peptides may function as neuroendocrine regulatory agents.