The last few decades have seen the birth and maturation of the field of Molecular Biology. Initially, mutant genes were focal points of genome exploration. Now, entire genomes are routinely sequenced, and the resident genes are automatically identified by annotation algorithms. Alternatively, proteomic approaches prepare proteolytic peptides of whole-cell extracts for analysis by mass spectrometry. Each of these approaches are strongly biased for large genes: large genes are frequent targets for mutation, long-open- reading frames are easily discerned in genomic sequence, and large proteins generate many peptides for mass spectrometry identification. This unintended bias has also created a large gap in our understanding of molecular biology. Recent work in eukaryotes and prokaryotes alike have uncovered multitudes of small genes or their encoded proteins. The numbers of small proteins (considered as 50 aa or less) rival that of traditionally large proteins, yet only a handful have been ascribed a function. The goal of this proposal is to propel this nascent field forward by facilitating both small protein discovery and functional characterization. We will develop and apply our small protein approaches in mycobacteria. Mycobacteria offer many advantages for small protein study. Foremost is that they express >1000 small proteins in standard conditions. The goal of this supplement is to support an outstanding undergraduate student, Lauren Fox, who aspires to be a research scientist, with direct hands-on laboratory research experience. Lauren will focus on dissecting the mechanism of regulation mediated by a unique set of sproteins involved in cysteine homeostasis. She will learn new technical and analytical skills, and develop a greater understanding of what it takes to be a research scientist. Involvement in the Wadsworth summer research program for undergraduates will further expose Lauren to potential careers in science, future mentors and new friends and colleagues.