It has been suspected for many years that cattle possess two functional IgH gene loci, located on Bos taurus autosome (BTA) 21 and BTA11, respectively. In this study, based on fluorescence in situ hybridization and additional experiments, we showed that all functional bovine IgH genes were located on BTA21, and only a truncated μCH2 exon was present on BTA11. By sequencing of seven bacterial artificial chromosome clones screened from a Hostein cow bacterial artificial chromosome library, we generated a 678-kb continuous genomic sequence covering the bovine IGHV, IGHD, IGHJ, and IGHC genes, which are organized as IGHVn-IGHDn-IGHJn-IGHM1-(IGHDP-IGHV3-IGHDn)3-IGHJn-IGHM2-IGHD-IGHG3-IGHG1-IGHG2-IGHE-IGHA. Although both of two functional IGHM genes, IGHM1 and IGHM2, can be expressed via independent VDJ recombinations, the IGHM2 can also be expressed through class switch recombination. Likely because more IGHD segments can be involved in the expression of IGHM2, the IGHM2 gene was shown to be dominantly expressed in most tissues throughout different developmental stages. Based on the length and identity of the coding sequence, the 23 IGHD segments identified in the locus could be divided into nine subgroups (termed IGHD1 to IGHD9). Except two members of IGHD9 (14 nt in size), all other functional IGHD segments are longer than 30 nt, with the IGHD8 gene (149 bp) to be the longest. These remarkably long germline IGHD segments play a pivotal role in generating the exceptionally great H chain CDR 3 length variability in cattle.

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Fan-shaped, naked amoebae are commonly encountered in samples from freshwater and marine habitats suggesting that they are an important component of the microbial food web. However, there are considerable problems in both detecting these amoebae and identifying them, given their morphological similarity. In this study we used restriction analysis and partial sequence analysis of the small-subunit 18S ribosomal RNA gene to examine the phylogenetic relationships between nine "fan-shaped" Vannella and Platyamoeba species. The molecular phylogeny showed that the marine Vannella and Platyamoeba isolates are closely related, whereas the freshwater isolates are disparate. Thus, the current reliance on the fine structure of the cell coat (glycocalyx) used to separate these genera is not justified. The study also highlights sequence elements that might be targeted by fluorescent probes for the direct detection of these amoebae in field samples. The molecular data were also used to aid the identification of three unknown fan-shaped isolates. All three unknowns resembled Vannella or Platyamoeba. However, one of the strains (a small < 10 microm, benthic, fan-shaped amoeba) probably represents a new genus.

Modeling of disease pathogenesis and immunity often is carried out in large animals that are natural targets for pathogens of human or economic relevance. Although murine mAbs are a valuable tool in identifying certain host͞pathogen interactions, progress in comparative immu-

We report the cloning and analysis of a bovine JH locus comprising a DQ52 segment, six JH segments and sequence to a 5' H chain intronic enhancer. The contig was mapped to BTA 11 and evidence was found for rearrangement of the sixth JH segment at a low but detectable frequency. In contrast, the fourth segment present at a second copy of the bovine JH locus mapping to BTA 21 was found to rearrange at high-frequency, forming FR4 in the majority of bovine Ig H chains. The data thus show that bovine H chains can be generated from segments at two distinct genomic locations. Further investigation should establish if rearrangement takes place at each locus or if the participating segments are brought together from different chromosomal locations by less conventional processes (for example by gene conversion or trans-chromosomal rearrangement).

The primary and secondary structure of the small-subunit ribosomal RNA (ssrRNA) gene from the naked, marine amoeba, Vannella anglica (subclass Gymnamoebia), was determined. The ssrRNA is 1962 nucleotides in length, with a low G+C content of 37.1%. The ssrRNA is composed of several uncommon secondary structure features including helix E8-1, which may be a useful target for rRNA probes for the direct identification of isolates in mixed culture. Phylogenetic analysis of sequence data showed that V. anglica branched prior to the rapid diversification of the eukaryotes. It did not associate with the other naked, lobose amoebae represented by Acanthamoeba and Hartmannella, indicating that Vannella represents a separate amoeboid lineage and the subclass Gymnamoebia is polyphyletic.

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