1. The bovine ti-casein gene has been isolated as a series of overlapping I clones and shown to consist of five exons distributed over a total length of approximately 13 kb. Most of the mature protein-coding sequence is contained in a single large exon.2. Approximately 65% of the gene has been sequenced together with portions of the 5'-and 3'-flanking sequences. The immediate 5'-flanking sequence contains several motifs which are characteristic of upstream regions including a TATA box, a CAAT box, a sequence similar to that recognized by transcription factor AP-1 and a purine-rich sequence resembling that found upstream in all other lactoprotein genes. Other possible regulatory sequences are found upstream of exon 4.3. The organization of the K-casein gene, together with its upstream sequence, confirms previous conclusions that it is unrelated to the calcium-sensitive-casein gene familiy to which it is linked. Evidence is presented which supports a previous suggestion that ic-casein and the fibrinogens are evolutionarily related.4. Intron sequences contain several examples of the A family of the artiodactyl Alu-like repeated sequences, together with a single example of a C-family sequence. The remainders of the introns of the rc-casein gene, compared with the repeat elements and exons, are A + T-rich.5. Among the I clones isolated, representatives were found of the A and B genetic variants which can be distinguished by restriction-enzyme analysis. Several other examples of polymorphisms in the non-coding region were found.The caseins are the predominant proteins in the milk of most species. As well as being the main source of amino acids for the suckling infant, the caseins serve to raise the calcium and phosphate concentrations in milk to levels well in excess of the solubility product of calcium phosphate by forming loosely ordered aggregates, termed micelles, which sequester calcium phosphate. Bone formation in the young animal thus depends on the ability of casein to transport appropriate quantities of calcium phosphate in milk.In bovine milk more than 20 individual components can be resolved when whole casein is analyzed electrophoretically under dissociating conditions [I]. These result from posttranslational modification and genetic variation of four primary translation products which correspond to asl-, clS2-, pand k--caseins. The xsl-, xs2-and p-caseins are insoluble in the presence of calcium ion at the concentrations at which it occurs in milk and these caseins are referred to as the calciumsensitive caseins. In contrast, K-casein is insensitive to the presence of calcium and is referred to as the micelle stabilizer because it is essential for the formation of stable casein micelles [2]. Following ingestion, the caseins are immobilized in the stomach as a result of clot formation. This occurs when chymosin (rennin) or pepsin specifically cleaves a single PheMet bond in K-casein to form insoluble para-K-casein (105 residues) and a soluble macropeptide containing the C-termind 64 amino acid residues of ...

Blattella germanica densovirus (BgDNV) is an autonomous parvovirus that infects the German cockroach. BgDNV possesses three mRNAs for NS proteins, two of which are splice variants of the unspliced transcript. The unspliced variant encodes open reading frame 5 (ORF5) (NS3), while NSspl1 encodes ORF3 (NS1) and ORF4 (NS2) and NSspl2 encodes the C-proximal half of NS1. BgDNV possesses three VP transcripts, one of which (VP) is unspliced, while the other two (VPspl1 and VPspl2) are generated by alternative splicing. The unspliced VP transcript contains both ORF1 and ORF2, while in VPspl1, ORF1 and ORF2 are joined in frame. The transcription of NS genes begins at an earlier stage of the virus life cycle than the transcription of VP genes. NS and VP transcripts overlap by 48 nucleotides (nt). BgDNV is characterized by two additional NS transcripts overlapping by more than 1,650 nt with VP-coding transcripts. Four different bands (97, 85, 80, and 57 kDa) corresponding to three BgDNV capsid proteins were detected on SDS-PAGE. Mass spectrometry analysis showed that the amino acid composition of the 85-kDa and 80-kDa proteins is the same. Moreover, both of these proteins are ubiquitinated. The BgDNV PLA 2 domain, which is critical for cellular uptake of the virus, is located in ORF2 and is present only in VP1. In contrast to all of the parvoviruses studied in this respect, VP2 has a unique N terminus that is not contained within VP1 and VP3. In situ recognition with NS1-and VP-specific antibodies revealed an uneven pattern of NS1 expression resembling a halo within the nuclear membrane.The Parvoviridae family comprises animal viruses which are among the smallest and most simply organized and are characterized by linear, single-stranded DNA (ssDNA) genomes encapsidated in 18-to 26-nm nonenveloped icosahedral capsids (9, 18). This family consists of two subfamilies, Parvovirinae and Densovirinae. Densoviruses (densonucleosis viruses or DNVs) are autonomously replicating parvoviruses pathogenic to invertebrates, in particular arthropods (60). Some DNVs are highly species specific, for instance, Galleria mellonella DNV (GmDNV) and Acheta domesticus DNV (AdDNV), which is probably explained by their strict dependence on host cell functions (replication, expression); other DNVs, such as Junonia coenia DNV (JcDNV) and Mythimna loreyi DNV (MlDNV), are polyspecific. Some DNVs, such as GmDNV and JcDNV, infect many tissues (polytropic), whereas others are monotropic (e.g., Bombyx mori DNV [BmDNV]). Almost all DNVs are usually fatal to their hosts (50). About 30 DNVs have been described so far, their hosts belonging to seven orders of the class Insecta and one order of the class Crustacea (45,50,51,55,61).Several distinctive features of DNVs, such as high virulence and host specificity, failure to infect vertebrates, and high resistance to extreme environmental conditions, make them potentially effective biological-control agents against populations of agriculturally and medically important pests. Moreover, DNVs could serve as convenie...

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The molecular mechanisms of the transposition of non-long terminal repeat (non-LTR) retrotransposons are not well understood; the key questions of how the 3′-ends of cDNA copies integrate and how site-specific integration occurs remain unresolved. Integration depends on properties of the endonuclease (EN) domain of retrotransposons. Using the EN domain of the Drosophila R2 retrotransposon as a model for other, closely related non-LTR retrotransposons, we investigated the EN domain and found that it resembles archaeal Holliday-junction resolvases. We suggest that these non-LTR retrotransposons are co-transcribed with the host transcript. Combined with the proposed resolvase activity of the EN domain, this model yields a novel mechanism for site-specific retrotransposition within this class of retrotransposons, with resolution proceeding via a Holliday junction intermediate.

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