Mutation patterns in the chemokine CXC receptor 4 gene subfamily.

Six representative CXCR4 mRNAs of fish, amphibia, birds, and mammals were selected to study the pattern of conservation/mutation of the individual nt of the coding sequences. According to an arbitrary conservation index ranging from 1 to 6, the indexes of conservation were: 5.04 for the first nt of coding triplets; 5.34 for the second nt of triplets, and 3.75 for the third nt of triplets. The average conservation index of the individual triplets was 4.71. The conservation index of the seven hydrophobic transmembrane domains was 5.60, while the cumulative conservation index of the intracytoplasmic and extracellular domains was 4.63. Separate autocorrelation and power spectral analyses of the series of conservation indexes for the first nt, the second nt and the triplets demonstrated a modest "basic" positive correlation for about the first 20 lags and accordingly some power concentration at the lower frequencies (long periods). Within the triplets, the correlation was studied between the conservation indexes of nt 1 and 2, 1 and 3, and 2 and 3. Correlations of 1 with 3 and 2 with 3 were positive, but in the range of the basic local correlation, whereas the correlation between the first and second nt was significantly higher. This correlation, together with the higher conservation of the second nt as compared to the first (two patterns also found in the formyl peptide receptors), are likely to have been established by selection processes directed towards a functional conservation or a "functional repair."

Decrease in resting calcium and calcium entry associated with slow-to-fast transition in unloaded rat soleus muscle.

Using fura-2 and the manganese quenching technique, we show here that sarcolemmal permeability to cations (SP-Ca) of slow-twitch muscles is greater than that of fast-twitch ones. This appears to be related to a higher expression and/or activity of stretch-activated channels, whereas leak channel activities are similar. During hindlimb suspension (HU), we found highly correlated decreases in SPCa and resting calcium of soleus muscle toward values of extensor digitorum longus (EDL) muscle. This was significant as soon as 3 days of suspension, contrary to soleus muscle caffeine sensitivity and responsiveness that were not modified after this HU period. After 14 days of HU, SP-Ca, resting calcium, and caffeine response of soleus muscle became similar to that normally observed in EDL muscle. These results demonstrate that the correlated decreases in SP-Ca and resting calcium precede most functional changes due to HU. Given the known shortening of HU soleus muscle, we proposed that this could induce a decrease of SP-Ca and a consequent reduction of resting calcium. According to the crucial role of resting cytosolic free calcium in the maintenance and the adaptation of muscle phenotype, our results suggest that slow-to-fast transition of HU soleus muscle is calcium dependent.

Mutation, selection and the amino acid hydropathic character: a study on receptor genes involved in immune and non-immune functions.

In some mRNA sequences, namely those of formyl peptide receptors and chemokine CXC receptors 4, it has been observed that the second nucleotide (nt) of the coding triplets is significantly more highly conserved than the first nt and the correlation between the conservation indexes of the first two nt is positive and significantly higher than the "basic" correlation usually found between adjacent nt. A theoretical analysis demonstrated that random mutations in the first nt preserve hydrophobicity in 73 % of triplets coding for hydrophobic amino acids (aa) and hydrophilicity in 77 % of triplets coding for hydrophilic aa, while random mutations in the second nt preserve hydrophobicity in 18 % of triplets coding for hydrophobic aa and hydrophilicity in 53 % of triplets coding for hydrophilic aa. When the triplets which had changed their hydropathic aa coding character underwent a second random mutation in the previously unmutated first or second nt, an additional 11 % of the originally hydrophobic-coding triplets reverted to hydrophobicity and an additional 14 % of the originally hydrophilic-coding triplets reverted to hydrophilicity. This analysis provides a rationale for why a higher number of mutations in the second nt are presumably negatively selected and a number of double mutations in the first and second nt presumably are positively selected, in cases when a mutation in one of the two is not reverted.

The HIV-1 Rev binding family of proteins: the dog proteins as a study model.

Various proteins that are required for the building of new complete human immunodeficiency type 1 virions (HIV-1) are coded by unspliced or partly spliced virus-derived mRNAs. HIV-1 has developed special strategies for moving these mRNAs to the cytoplasm to be translated. In the nucleus of the infected cell the virus-derived protein Regulator of expression of viral proteins (Rev) can bind both the viral intron-containing mRNAs and the cellular co-factor HIV-1 Rev binding protein (HRB) and this complex may be shuttled through the nuclear pores. HRB genes have been relatively well conserved during evolution, from Drosophila to humans. However, as a consequence of reading-frame shifts due to nt insertions/deletions, the protein products generated may differ considerably from the prototypal HRB protein, which comprises one Arf-GAP zinc finger domain, several Phenylalanine-Glycine (FG) motifs and four Asparagine-Proline-Phenylalanine (NPF) motifs. This variability is best exemplified by four HRB proteins of the dog, which are discussed here in more detail. The hypothesis is advanced that atypical HRB proteins may not be able to bind Rev and possibly have other, still undetermined, functions. Since the cellular co-factor HRB is essential for viral replication and spread but is not required for cell viability and main bodily functions, it might be an attractive candidate for anti-HIV-1 drug targeting.