COMPUTER-BASED METHODOLOGY FOR SYSTEM DEVELOPMENT: SITE PRODUCTION AND REDUCTION SYSTEM

A biological model, the nervous system, is applied to a man–machine system in order to stimulate interdisciplinary thought. Conceptual similarities between engineering, communication, and psychology are examined as they relate to the application of this model. If system designers incorporate afferent (Exercise) and efferent (Evaluation) subsystems so that feedback capability exists, system “learning” becomes feasible. This biological model is operational in the Site Production and Reduction System (SPARS), a computer system providing support for system training in the Semi-Automatic Ground Environment (SAGE) System. SPARS problem production (Exercise) and data reduction (Evaluation) capabilities are described and implications for future system technology are presented.

Control of aspartate transcarbamylase activity in type 5 adenovirus-infected HeLa cells

Consigli, Richard A. (University of Pennsylvania, Philadelphia), and Harold S. Ginsberg. Control of aspartate transcarbamylase activity in type 5 adenovirus-infected HeLa cells. J. Bacteriol. 87:1027-1033. 1964.-Type 5 adenovirus infection induces increased aspartate transcarbamylase (ATCase) activity during the period of magnified nucleic acid biosynthesis. Increased activity can be prevented by addition of pyrimidines to the culture medium. ATCase in HeLa cells is regulated by feedback inhibition, and purified enzyme can be inhibited in vitro by cytidine triphosphate (CTP). The enzyme from infected cells has a pH optimum, maximal velocity, and K(m) for aspartate distinctly different from ATCase from control cells. However, heating of ATCase from uninfected cells converts the enzyme so that its characteristics are identical with enzyme from infected cells. Conversely, addition of CTP to ATCase from infected cells changes the characteristics of the enzyme so that they are the same as those of enzyme from uninfected cells. The evidence presented suggests that increased nucleic acid biosynthesis in infected cells initiates a release from feedback inhibition and increases ATCase activity by reducing the concentration of pyrimidines and purines in the acid-soluble pool.