The Effects of Temperature and Body Mass on Jump Performance of the Locust Locusta migratoria

Locusts jump by rapidly releasing energy from cuticular springs built into the hind femur that deform when the femur muscle contracts. This study is the first to examine the effect of temperature on jump energy at each life stage of any orthopteran. Ballistics and high-speed cinematography were used to quantify the energy, distance, and take-off angle of the jump at 15, 25, and 35°C in the locust Locusta migratoria. Allometric analysis across the five juvenile stages at 35°C reveals that jump distance (D; m) scales with body mass (M; g) according to the power equation D = 0.35M ^{0.17±0.08 (95% CI)}, jump take-off angle (A; degrees) scales as A = 52.5M ^0.00±0.06, and jump energy (E; mJ per jump) scales as E = 1.91M ^1.14±0.09. Temperature has no significant effect on the exponent of these relationships, and only a modest effect on the elevation, with an overall Q₁₀ of 1.08 for jump distance and 1.09 for jump energy. On average, adults jump 87% farther and with 74% more energy than predicted based on juvenile scaling data. The positive allometric scaling of jump distance and jump energy across the juvenile life stages is likely facilitated by the concomitant relative increase in the total length (L _f+t; mm) of the femur and tibia of the hind leg, L _f+t = 34.9M ^0.37±0.02. The weak temperature-dependence of jump performance can be traced to the maximum tension of the hind femur muscle and the energy storage capacity of the femur''s cuticular springs. The disproportionately greater jump energy and jump distance of adults is associated with relatively longer (12%) legs and a relatively larger (11%) femur muscle cross-sectional area, which could allow more strain loading into the femur''s cuticular springs. Augmented jump performance in volant adult locusts achieves the take-off velocity required to initiate flight.     

Tetrahymena contain two distinct and unusual high mobility group (HMG)- like proteins

Previous studies have described the existence of high mobility group (HMG)-like proteins in macronuclei of the ciliated protozoan, Tetrahymena thermophila (Hamana, K., and K. Iwai, 1979, J. Biochem. [Tokyo], 69:1097-1111; Levy-Wilson, B., M. S. Denker, and E. Ito, 1983, Biochemistry, 22:1715-1721). In this report, two of these proteins, LG- 1 and LG-2, have been further characterized. Polyclonal antibodies raised against LG-1 and LG-2 fail to cross react with each other or any other macronuclear polypeptide in immunoblotting analyses. As well, LG- 1 and LG-2 antibodies do not react with calf thymus, chicken, or yeast HMG proteins. Consistent with these results, a 47 amino-terminal sequence of LG-1 has been determined that shows limited homology to both calf thymus HMGs 1 and 2 and HMGs 14 and 17. Two internal sequences of V8 protease-generated peptides from LG-2 have been determined, and these do not share any homology to the LG-1 sequence or any other sequenced HMG proteins. Comparison of the partial sequences of LG-1 and LG-2 with the complete amino acid sequence of the Tetrahymena histone H1 (Wu, M., C. D. Allis, R. Richman, R. G. Cook, and M. A. Gorovsky, 1986, Proc. Natl. Acad. Sci. USA, 83:8674-8678) rules out the possibility that LG-1 and LG-2 are proteolytically derived from H1, the other major macronuclear perchloric acid-soluble protein. Interestingly, however, both LG-1 and LG-2 are efficiently extracted from macronuclei by elutive intercalation (Schroter, H., G. Maier, H. Ponsting, and A. Nordheim, 1985, Embo (Eur. Mol. Biol. Organ.) J., 4:3867-3872), suggesting that both may share yet undetermined properties with HMGs 14 and 17 of higher eukaryotes. Examination of the pattern of LG-1 and LG-2 synthesis during the sexual phase of the life cycle, conjugation, demonstrates that the synthesis of LG-1 and LG-2 is coordinately increased from basal levels during the differentiation of new macronuclei (7-13 h), suggesting that both of these proteins play a role in determining a macronuclear phenotype. However, a specific induction of LG-2 synthesis is detected in early stages of conjugation (meiotic prophase, 1-4 h), leading to maximal synthesis of LG-2 at 3 h. Interestingly, the early induction of LG-2 synthesis closely parallels the hyperphosphorylation of histone H1. Taken together, these data suggest that LG-1 and LG-2 are not strongly related to each other or to higher eukaryotic HMG proteins.(ABSTRACT TRUNCATED AT 400 WORDS)     

tRNA recognition site of Escherichia coli methionyl-tRNA synthetase

We have previously shown that anticodon bases are essential for specific recognition of tRNA substrates by Escherichia coli methionyl-tRNA synthetase (MetRS) [Schulman, L. H., & Pelka, H. (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 6755-6759] and that the enzyme tightly binds to C34 at the wobble position of E. coli initiator methionine tRNA (tRNAfMet) [Pelka, H., & Schulman, L. H. (1986) Biochemistry 25, 4450-4456]. We have also previously demonstrated that an affinity labeling derivative of tRNAfMet can be quantitatively cross-linked to the tRNA binding site of MetRS [Valenzuela, D., & Schulman, L. H. (1986) Biochemistry 25, 4555-4561]. Here, we have determined the site in MetRS which is cross-linked to the anticodon of tRNAfMet, as well as the location of four additional cross-links. Only a single peptide, containing Lys465, is covalently coupled to C34, indicating that the recognition site for the anticodon is close to this sequence in the three-dimensional structure of MetRS. The D loop at one corner of the tRNA molecule is cross-linked to three peptides, containing Lys402, Lys439, and Lys596. The 5' terminus of the tRNA is cross-linked to Lys640, near the carboxy terminus of the enzyme. Since the 3' end of tRNAfMet is positioned close to the active site in the N-terminal domain [Hountondji, C., Blanquet, S., & Lederer, F. (1985) Biochemistry 24, 1175-1180], this result indicates that the carboxy ends of the two polypeptide chains of native dimeric MetRS are folded back toward the N-terminal domain of each subunit.     

In vivo and in vitro phosphorylation of murine lymphocyte differentiation antigen CD5

Ly-1, the murine lymphocyte differentiation antigen CD5, is phosphorylated constitutively in vivo. This phosphorylation is enhanced by phorbol 12-myristate 13-acetate (PMA) treatment, but not by concanavalin A, Ca2+ ionophore or dibutyryl cAMP. Prolonged PMA treatment abolished PMA-induced Ly-1 phosphorylation but not constitutive phosphorylation, suggesting that protein kinase C (PKC) is responsible for this enhanced phosphorylation, but not the basal phosphorylation of Ly-1. Ly-1 is phosphorylated by PKC added to membranes, further supporting a role for protein kinase C in the in vivo phosphorylation of Ly-1.     

"Rates" of birth defects

The proportion of children born with a particular defect is not a "birth defect rate" but, rather, a prevalence proportion. The implications of confusing a rate and a proportion are discussed in terms of the interpretation of birth defect data. It is recommended that "prevalence proportion" or "prevalence" be used to report the frequency of various defects rather than the often-used "prevalence rate."