On the Treatment of Optimization Problems With L1 Penalty Terms via Multiobjective Continuation.

We present a novel algorithm that allows us to gain detailed insight into the effects of sparsity in linear and nonlinear optimization. Sparsity is of great importance in many scientific areas such as image and signal processing, medical imaging, compressed sensing, and machine learning, as it ensures robustness against noisy data and yields models that are easier to interpret due to the small number of relevant terms. It is common practice to enforce sparsity by adding the l-norm as a penalty term.

One of three transmembrane stretches is sufficient for the functioning of the SecE protein, a membrane component of the E. coli secretion machinery.

The E. coli secE (prlG) gene codes for an integral cytoplasmic membrane protein which is part of the cell's secretory machinery. A deletion of nearly the entire gene renders the cell dependent on the presence of a complementing secE+ plasmid, indicating that the SecE protein is essential for growth.

The genetics of protein secretion in E. coli.

Genetic studies have identified six genes whose products comprise the general protein secretion machinery of Escherichia coli. Insights from mutant analysis and the biochemical properties of the purified components allows the secretion pathway to be described in some detail. The picture emerging provides a useful paradigm for similar pathways in other organisms.

The sec and prl genes of Escherichia coli.

Two general approaches have been used to define genetically the genes that encode components of the cellular protein export machinery. One of these strategies identifies mutations that confer a conditional-lethal, pleiotropic export defect (sec, secretion). The other identifies dominant suppressors of signal sequence mutations (prl, protein localization).

PrlA (SecY) and PrlG (SecE) interact directly and function sequentially during protein translocation in E. coli.

Three strategies for genetic analysis show that two inner membrane components of the export machinery, PrlA (SecY) and PrlG (SecE), interact directly while catalyzing the translocation of secreted proteins across the cytoplasmic membrane of E. coli. The first, suppressor-directed inactivation (SDI), exploits the specific interaction between dominant prl suppressors of signal sequence mutations and mutant LacZ hybrid proteins.