Given an abstract of a paper, generate a title for this paper such that conveys the key focus of the paper.

Q: Abstract: The crossing over in five murine I-region recombinants (Is/Ik) was studied by restriction fragment length polymorphism analysis after Southern blot hybridization by using I-region-specific probes. These recombinants included three recently developed strains, B10.ASR1, B10.ASR11, and B10.ASR12; and two strains B10.S(9R) and B10.HTT derived earlier. Although these recombinants were reciprocal in haplotype orientation to the three recombinants we reported recently, these too crossed over within the same 7 kb stretch of DNA in the E beta gene. This 7 kb stretch of DNA included the 3' half of the first intron, the beta 1 exon, the second intron, and the beta 2 exon. A comparison of the cDNA sequences of the two parental E beta alleles revealed that although the beta 2 exons were identical, there were several nucleotide differences between the two beta 1 exons. This allowed us to determine the parental origin of the beta 1 exon in the recombinants at the level of transcription by using S1 nuclease mapping. Thus we were able to show that in each case the 3' portion of the first intron and the beta 1 exon were upstream from the site of crossover. All eight recombinants involving the k and s haplotypes now can be mapped within a 4.5 kb stretch of DNA, which includes only the beta 1-beta 2 intron and the beta 2 exon of the E beta gene. These findings imply that the I-E molecules expressed in these recombinants will probably have conserved sequences and therefore will exhibit identical I-E-restricted immune responses, despite the fact that crossing over could have occurred at different sites within the beta 1-beta 2 intron.

A: Molecular mapping of murine I region recombinants. II. Crossing over in the E beta gene is restricted to a 4.5 kb stretch of DNA that excludes the beta 1 exon.
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Q: Abstract: The characteristic clinical and histological features of three cases of malignant eccrine poroma are discussed, in addition to the metastatic disease that had occurred in two cases. These cases were compared with previously reported cases of malignant eccrine poroma that had metastasised, and it is suggested that a strict classification of malignant eccrine sweat gland tumours should be made.

A: Malignant eccrine poroma: report of three cases.
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Q: Abstract: The amount and sources of T3 associated with high affinity, low capacity cellular nuclear receptors in brown adipose tissue (BAT) have been estimated by in vivo pulse-labeling techniques. Maximal binding capacity was measured by in vivo saturation analysis. Nuclear receptor occupancy at endogenous levels of T3 and T4 in euthyroid rats was estimated from the equilibrium nuclear to serum ratio of tracer T3, and the locally generated nuclear T3 to serum T4 ratio after injecting tracer T3 and T4. These ratios were multiplied, respectively, by the endogenous concentrations of T3 and T4 as measured by RIA. The maximal binding capacity was 0.65 ng T3/mg DNA, and saturation was 71%. Fifty-five percent of the nuclear T3 was generated locally, and 45% was derived from circulating T3. BAT is, hence, comparable to the liver in number of receptors (approximately 5000/cell) and to the pituitary with regard to saturation and relative contributions of locally generated T3 and plasma T3 to nuclear T3. These results suggest that BAT may be an important target for thyroid hormones and, along with other data, that alterations in the activity of the type II 5'-deiodinase of this tissue may influence the saturation of nuclear T3 receptors.

A:
Nuclear 3,5,3'-triiodothyronine (T3) in brown adipose tissue: receptor occupancy and sources of T3 as determined by in vivo techniques.
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