Abstract: Methods and systems of applying mass spectrometry to the analysis of peptides and amino acids, especially in the proteome setting. More particularly, the invention relates to a mass spectrometry-based method for detection of amino acid modifications, such as phosphorylation.

Abstract: The present invention provides improvements in the expression cloning method for isolating novel cDNA clones. In particular, in the expression cloning method comprising the steps of preparing a cDNA library from a cell that expresses a desired protein; inserting the cDNA library into an expression vector; inserting the cDNA library into bacterial cells and culturing the bacterial cells to produce individual bacterial colonies; collecting pools of a predetermined number of individual bacterial colonies; isolating the cDNAs contained in the pools; expressing proteins encoded by the cDNAs; and detecting the desired protein, positive clones may be efficiently and cost-effectively obtained by collecting pools of about 100 individual bacterial colonies and expressing proteins encoded by the cDNAs in the pools in vitro.