Extracellular calcium mimics the actions of platelet-derived growth factor on mouse fibroblasts.

Microprecipitates of calcium phosphate (CaPO4) can substitute for platelet-derived growth factor (PDGF) to stimulate the growth of cultured 3T3 cells. In two-part complementation assays, CaPO4 behaves as a PDGF-like "competence factor"--that is, the mitogenic response to CaPO4 is enhanced synergistically by "progression factors" contained in platelet-poor plasma. In studies described here, we show that early cytoplasmic and intranuclear events in the mitogenic response to CaPO4 are equivalent to those induced by PDGF. However, no net increase in tyrosine kinase activity of either the PDGF-alpha or PDGF-beta receptor is seen following exposure to CaPO4. Our data suggest that calcium acts within the cell, regulating events which normally proceed from activation of PDGF receptors. Alternatively, microprecipitates of CaPO4 could act externally by activating a growth factor receptor which escapes detection with available reagents.     

Transposition of the gene cluster CYC1-OSM1-RAD7 in yeast

A mutant of the yeast Saccharomyces cerevisiae contains an increased amount of iso-1-cytochrome c because two copies of a segment, denoted COR, were transposed to a new position on chromosome VII, while the original COR region was retained at the normal position on chromosome X; this COR segment encompasses the CYC1, OSM1 and RAD7 loci which determine, respectively, iso-1-cytochrome c, osmotic sensitivity and ultraviolet light sensitivity. The analysis of genomic DNA with cloned probes indicates that the length of the COR segment is approximately 12,000 base-pairs. We suggest that certain normal strains of yeast, which possibly may contain reiterated sequences, can produce extended transpositions similar to prokaryotes.     

Thyroid hormone modulation of agonist - beta-adrenergic receptor interactions in the rat heart

We have investigated alterations in beta-adrenergic receptors in rat myocardial membranes derived from hypothyroid and hyperthyroid animals. (-)Isoproterenol competition curves with (-)[³H]dihydroalprenolol revealed that isoproterenol binds to the beta-adrenergic receptor with two distinct affinity states having high (K_H) and low (K_L) dissociation constants. In the presence of guanine nucleotides the isoproterenol competition curve steepened and had a higher EC₅₀ (50% displacement). This was due to a transition of the high affinity state to a uniformly low affinity state. Using computer modeling of these competition curves, we have demonstrated that in hyperthyroidism, the isoproterenol curve in the absence of guanine nucleotides is shifted to the left with the EC₅₀ changing from 180 ± 40 to 80 ± 20 nM (p < .02). The fold shift (4 fold) in K_H (nM) 30 ± 9 to 7 ± 2 (p < .001) is greater than that (1.6 fold) in K_L (nM) 595 ± 56 to 376 ± 34 (p < .001) such that the K_L/K_H ratio shifted from 20 ± 3 to 54 ± 9 (p < .001). The ratio, K_L/K_H, for a particular agonist appears to be related to its efficacy in activating adenylate cyclase.There was no significant alteration in any of these parameters in hypothyroid animals. Receptor number was decreased in hypothyroidism, 16 ± 3 fmol/mg protein (p < .03) and increased in hyperthyroidism 44 ± 4 (p < .03) compared to control 26 ± 2.In the rat heart agonist affinity and receptor number are modulated in hyperthyroidism, but only receptor number in hypothryoidism. Thus thyroid hormone can modify not only receptor number but agonist affinity as well.     

RNA metabolism in apices of Pharbitis nil daring floral induction

RNA metabolism was studied in apices of Pharbitis nil duringand after floral induction. In continuous light ³H-uridine accumulatedin RNA at a constant rate over an 18 hr period. In darkness,however, the rate of accumulation of label into RNA was constantuntil the 10th hour at which time a rapid burst of accumulationoccurred, peaking at the 14th hour of darkness and followedby a net loss of label. The RNA involved in this burst is probablymRNA due to its size and poly(A) content. This phenomenon doesnot seem to be associated with floral induction, since the siteof perception is the apex, and it also occurs under conditionswhere floral initiation is inhibited by a brief light interruptionof the dark period. Immediately after floral induction by a16-hr dark period the rate of RNA synthesis was suppressed about14%. This suppression lasts for about 12 hr and was followedby a twofold increase in the rate of RNA synthesis, comparedto non-induced apices, at 64 hr after the beginning of the inductivedark period. These post-induction changes were found to occurin all RNA fractions. ¹Present address: Department of Radiation Biology and Biophysics,University of Rochester School of Medicine and Dentistry, Rochester,N.Y. 14642, U.S.A. (Received March 15, 1976; )     

Qualitative analysis by isoelectric focusing of the protein content of Pharbitis nil apices and cotyledons during floral induction

The protein content of apices and cotyledons in Morally inducedor vegetative plants of Pharbitis nilwas examined using isoelectricfocusing. No differences were found in the protein patternsproduced by apical tissue with and without floral induction.Cotyledons, however, repeatedly showed the distinct loss ofa single protein band on floral induction. ¹Current address: Department of Radiation Biology and Biophysics,The University of Rochester School of Medicine and Dentristry,Rochester, N.Y. 14642, U.S.A. (Received March 29, 1976; )     

Frequency and displacement amplitude relations for normal hand tremor.

Spectral analysis of hand tremor records obtained from normal subjects during continuous extension of the hand for 15-45 min revealed that the root-mean-square (rms) displacement amplitude of the tremor increased from control levels of about 30 mum to levels on the order of 100-1,000 times control. Associated with this increase in the displacement was a systematic decrease in the hand tremor frequency from control values of 8-9 Hz to values of 4-6 Hz. Spectral analysis of demodulated extensor EMG records indicated a consistent relation between EMG modulation amplitude at the tremor frequency and the tremor displacement amplitude for tremor records with rms displacement above about 100 mum. No consistent relation was found between these two variables for tremor records with displacements below 100 mum. Consideration of both mechanical and neural reflex effects indicated that a viscoelastic-mass mechanism primarily determined the small-amplitude (less than 100 mum) tremors, while the large displacement tremors may have involved both mechanical and neural feed back factors.     

Characterization of leucocin A-UAL 187 and cloning of the bacteriocin gene from Leuconostoc gelidum.

Leucocin A-UAL 187 is a bacteriocin produced by Leuconostoc gelidum UAL 187, a lactic acid bacterium isolated from vacuum-packaged meat. The bacteriocin was purified by ammonium sulfate or acid (pH 2.5) precipitation, hydrophobic interaction chromatography, gel filtration, and reversed-phase high-performance liquid chromatography with a yield of 58% of the original activity. Leucocin A is stable at low pH and heat resistant, and the activity of the pure form is enhanced by the addition of bovine serum albumin. It is inactivated by a range of proteolytic enzymes. The molecular weight was determined by mass spectrometry to be 3,930.3 +/- 0.4. Leucocin A-UAL 187 contains 37 amino acids with a calculated molecular weight of 3,932.3. A mixed oligonucleotide (24-mer) homologous to the sequence of the already known N terminus of the bacteriocin hybridized to a 2.9-kb HpaII fragment of a 7.6-MDa plasmid from the producer strain. The fragment was cloned into pUC118 and then subcloned into a lactococcal shuttle vector, pNZ19. DNA sequencing revealed an operon consisting of a putative upstream promoter, a downstream terminator, and two open reading frames flanked by a putative upstream promoter and a downstream terminator. The first open reading frame downstream of the promoter contains 61 amino acids and is identified as the leucocin structural gene, consisting of a 37-amino-acid bacteriocin and a 24-residue N-terminal extension. No phenotypic expression of the bacteriocin was evident in several lactic acid bacteria that were electrotransformed with pNZ19 containing the 2.9-kb cloned fragment of the leucocin A plasmid.