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Low-temperature protein metabolism: seasonal changes in protein synthesis and RNA dynamics in the Antarctic limpet Nacella concinna Strebel 1908

Keiron P. P. Fraser^*, Andrew Clarke and Lloyd S. Peck

Natural Environment Research Council, British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK

View larger version (11K): [in a new window]   Fig. 1. Intracellular free-pool phenylalanine specific radioactivities in Nacella concinna at Rothera Point, Antarctica in (A) February, (B) July, (C) October and (D) December. Measurements were made after flooding dose injections at time zero and are expressed as d.p.m. nmol-1 phenylalanine. All data points are means ± S.E.M. N=6, except for the last two data points of (B), (C) and (D), in which N=7.

View larger version (10K): [in a new window]   Fig. 2. Incorporation of radiolabelled phenylalanine into body protein of Nacella concinna at Rothera Point, Antarctica, after flooding dose injections at time zero. Data are expressed as d.p.m. nmol-1 phenylalanine. (A) February (y=0.0026x-0.0346, r2=0.58); (B) July (y=0.0022x-0.0747, r2=0.59); (C) October (y=0.004x-0.1147, r2=0.67); and (D) December (y=0.0054x-0.1986, r2=0.63), where y is the protein-incorporated specific radioactivity expressed as d.p.m. nmol-1, and x is the time in min. Data points are means ± S.E.M. N=6, except for the last two data points of (B), (C) and (D), in which N=7. All regression slopes are highly significant (P<0.001), with intercepts not significantly different from zero.

View larger version (10K): [in a new window]   Fig 3. Mass-standardised whole-body RNA:protein ratios plotted against temperature. All values were standardised to a mean body mass of 129 g, the mean body mass of all the animals in the data set, using a scaling coefficient of -0.24. The scaling coefficient was calculated by fitting a least-squares regression model to the natural-log-transformed body mass and RNA:protein ratio data for all species. The regression line relating temperature and RNA:protein ratio was fitted by least-squares regression analysis (y=10.4-0.274x, r2=0.20, P<0.05) to all data with the exception of points labeled 14 (rat). For sources of plotted data, see Table 2.

View larger version (11K): [in a new window]   Fig 4. Whole-body RNA translational efficiencies (kRNA) plotted against temperature. The plotted regression line was fitted by least-squares regression analysis (y=0.738+0.104x, r2=0.20, P<0.05) to all data within the data set. For sources of plotted data, see Table 3.