In order to study control ofDNA synthesis in complex eukaryotic systems, one would like to examine a single replicon whose time ofsynthesis within the S period is known. Certain cell lines contain amplified sequences that appear to replicate synchronously with respect to one another and therefore behave as ifthey were composed of one or a few replicon types (1, 2). These sequences are found in a variety of methotrexate (MTX)-resistant mouse and hamster cell lines, and arise through the amplification of a large segment which includes the gene for dihydrofolate reductase (DHFR; tetrahydrofolate dehydrogenase;

No abstract

The dendral computer program uses established rules of molecular fragmentation to help chemists solve complex structural problems from mass spectral data. This paper describes a computer program called Meta-DENDRAL, that can aid in the discovery of such rules from empirical data on known compounds. The program uses heuristic methods to search for common structural environments around those bonds that are found to fragment and abstracts plausible fragmentation rules. The program has been tested on the well-characterized, low-resolution mass spectra of aliphatic amines and the high-resolution mass spectra of estrogenic steroids. The program has also discovered new fragmentation rules for mono-, di-, and triketoandrostanes.

No abstract

No abstract