Characterization of a pollen-specific cDNA from sunflower encoding a zinc finger protein.

The maize transposable element Activator (Ac) carries subterminal CpG-rich sequences which are essential for the transposition of the element. It has previously been shown that the methylation of certain sequences contained in this region can alter their ability to interact with the Ac-encoded protein. The novel hypothesis that the methylation of subterminal Ac sequences is required for transposition was tested. Approximately 150 bp of the 5' subterminal region of the Ac element was examined for the presence of 5-methylcytosines by the ligation-mediated polymerase chain reaction (LMPCR)-aided genomic sequencing method. The methylation status of 22 and 39 cytosines on either strand of the DNA were analysed in each of five different transgenic tobacco cultures carrying transposable Ac sequences. Ten micrograms of tobacco DNA were used for each base-specific cleavage reaction before amplification by LMPCR. All but one of the cytosines were unmethylated. Only a minor fraction of the Ac molecules was methylated at one cytosine residue. It is concluded that DNA methylation at the tested Ac sequences is not required for the transposability of Ac or Ds elements in tobacco cells.     

Convergent Adaptations to Cave Life in the Rhamdia Laticauda Catfish Group (Pimelodidae, Teleostei)

The nocturnal Mexican catfish Rhamdia laticauda (Pimelodidae, Teleostei) is the surface sister species of a number of cave species. Comparison between two of them, R. zongolicensis and R. reddelli, reveals an intermediate state of reduction of the biologically functionless eyes, melanin pigmentation and the negative phototactic behavior. The surface species is perfectly adapted to life in darkness. Therefore only few constructive adaptations are developed in the cave species. For survival under conditions of low food supply in the caves the barbels are elongated to improve the senses of taste and touch and more fat can be deposited in the cave fish tissue. Due to convergent evolution the two cave species are morphologically much alike and show only minor diagnostic meristic differences. From geological data it can be concluded that the two cave species started troglobitic evolution at the end of Pleistocene.