Time-dependent AluI action on human chromosomes.

We have analyzed the pattern of AluI digestion over time on human chromosomes in order to monitor the evolution of the in situ enzyme action. Short treatments followed by Giemsa staining produce a G-like banding effect, whereas longer treatments produce a C-like banding pattern. However, when Propidium iodide staining is used, it reveals a uniform bright fluorescence after short AluI digestions and C bands when longer treatments are developed. We propose that C banding is the result of a uniform DNA removal in non centromeric regions taking place after a critical time point, the initial G like banding being produced by changes in the DNA-proteins interactions.

An acidic silver staining method for synaptonemal complexes under light microscopy.

A simple method is presented by which synaptonemal complexes (SCs) can be visualized under bright field microscopy. Staining was accomplished with a silver nitrate solution adjusted to pH 3-3.5 with formic acid, after an acidic fixation. This method is suitable for the demonstration of SCs, centromeres and NOR regions in both mammalian (Rattus norvegicus, 'Wistar') and orthopteran spermatocytes (Steropleurus martorelli complex). Results suggest that pretreatment with solutions of alkaline pH are not needed for demonstrating SCs, and that the silver impregnation may also operate when the proteinaceous lateral elements of the SC are subjected to low pH conditions. Differential staining of the X chromosome during meiosis in Orthoptera, and a core-like structure in the chromosomes during the more condensed stages of meiosis and mitosis can also be shown.