o identify fast-moving fields, Science Watch has been digging through ISI's Research Front Database for 1999. Each research front, or "cluster" of papers, is an active specialty area consisting of a group of related publications that are frequently co-cited by current journal articles. The cited works, representing the intellectual foundations of the field, are called the "core" of the specialty, or research front. The presence of many recent papers within a core indicates a hot field–a specialty area undergoing rapid transformation.

As in its previous roundup of hot research fronts (see 9[1]:1-2, January/February 1998), Science Watch has divided the specialty fields into two broad groupings. The table above lists biomedical fields, each having at least 11 core papers. Hot fields in the physical sciences, with at least eight core papers each, are listed on the next page. In both, the tables are ranked by "newness," according to the average age of the cluster's foundation papers. In other words, fields with the higher percentage of recent core papers–those published in 1998 and 1999–receive priority.

The next page also features a ranking of "superhot" fields: six specialty areas whose cores, although smaller than those in the other tables (with at least six papers each), contain the very highest proportions of recent papers.

Heading the list of biomedical fields is a specialty area dealing with human homologues of the Drosophila Toll receptor. Variations of this molecule, and the immune-system signaling pathway of which it is a part, help to govern immune response in vertebrates and invertebrates, also functioning in the disease-resistance genes seen in many plants. As one of this front's core authors, Howard Hughes Medical Institute investigator Charles H. Janeway, has observed, the Toll pathway appears to have been evolutionarily conserved for more than a billion years. The core papers in this front examine various aspects of human "toll-like receptors" or TLRs.

Not surprisingly, given its prominence in these pages in recent years, the topic of apoptosis, or programmed cell death, also ranks high on the list of hot biomedical fields. A comparatively large research front, with a core of 25 papers, anchors this specialty. Some of these papers examine the actions of caspases, the protein group that plays an essential role in the process of cell death. Others focus on the protein Bcl-2 and its interaction with the apoptosis-inducing agent cytochrome c, which is released from cellular mitochondria. One of these core papers, a 1998 Cell report on the protein bid, which interacts with Bcl-2, is currently at #6 in the Biology Top Ten of this issue.

The biomedical list also reflects recent activity in genomics and the use of databases and automated methods to identify and evaluate genetic and protein sequences. One research front encompasses a variety of protein-sequence databases. Two of this front's core papers, on the GenBank database (see D.A. Benson, et al., Nucl. Acids Res., 27[1]:12-7, 1 January 1999) and the SWISS-PROT data bank (see A. Bairoch and R. Apweiler, Nucl. Acids. Res., 27[1]:49-54, 1 January 1999) made recent appearances in the Biology Top Ten. Another research front centers on the use of DNA microarrays–sometimes referred to as "DNA chips"–to perform detailed analyses of variations in gene expression in cancers and other conditions. The third of these related clusters deals with the whole-genome sequences of microbial life forms. Its core papers present the sequences (and, in some instances, comparative analysis) of the gastric pathogen Helicobacter pylori, the gram-positive bacterium Bacillus subtilis, the archaeon Archaeoglobus fulgidus, and others.
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