THE following list of chromosome numbers is a combination of the studies of Dr Moffett on grasses of Rhodesia and Miss Hurcombe on grasses of the provinces of the Union of South Africa. Dr Moffett's species were identified by Miss K. Sturgeon of the Department of Agriculture, Salisbury, Southern Rhodesia; Miss Hurcombe's species were grown from seed supplied by Miss Wilman through the Director, Royal Botanic Gardens, Kew, or roots were sent directly from South Africa, and specimens of these have been preserved in the Kew Herbarium (Editor). Notes after the numbers refer to comparison with previous counts given in the Chromosome Atlas where the full references to the original papers will be found.

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I. INTRODUCTION Two closely-related species of Acacias, A. decurrens or green wattle and A. mollissima or black wattle, are grown in the Union of South Africa for tannin production. Green wattle, although generally considered hardier under adverse conditions, does not produce so high a quality of tannin. The small proportion of green wattle previously under cultivation has therefore now been largely replaced by black wattle. From the genetical point of view, however, green wattle has one marked advantage: the seed ripens some four months after flowering, as opposed to fourteen months in black wattle. Philp and Sherry (1946) therefore chose green wattle for their preliminary work on the degree of natural crossing in wattle and they were able to show that the species was largely cross-pollinated. Because of the close resemblance between the two species, they suggested that black wattle would also prove to be largely cross-pollinated. Selfed progeny from several black wattle trees have now been grown and scored for recessive seedling characters and it has been possible to calculate the approximate amount of natural crossing in many of these trees. 2. METHODS Selfed and natural (open-pollinated) progenies were grown from 26 trees from various parts of the wattle-growing area. The method of bagging followed that of Philp and Sherry (bc. cit.), cellophane bags being used throughout. Bagging was

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The Locus Control Region (LCR) requires intronic elements within β-globin transgenes to direct high level expression at all ectopic integration sites. However, these essential intronic elements cannot be transmitted through retrovirus vectors and their deletion may compromise the therapeutic potential for gene therapy. Here, we systematically regenerate functional β-globin intron 2 elements that rescue LCR activity directed by 5′HS3. Evaluation in transgenic mice demonstrates that an Oct-1 binding site and an enhancer in the intron cooperate to increase expression levels from LCR globin transgenes. Replacement of the intronic AT-rich region with the Igμ 3′MAR rescues LCR activity in single copy transgenic mice. Importantly, a combination of the Oct-1 site, Igμ 3′MAR and intronic enhancer in the BGT158 cassette directs more consistent levels of expression in transgenic mice. By introducing intron-modified transgenes into the same genomic integration site in erythroid cells, we show that BGT158 has the greatest transcriptional induction. 3D DNA FISH establishes that induction stimulates this small 5′HS3 containing transgene and the endogenous locus to spatially reorganize towards more central locations in erythroid nuclei. Electron Spectroscopic Imaging (ESI) of chromatin fibers demonstrates that ultrastructural heterochromatin is primarily perinuclear and does not reorganize. Finally, we transmit intron-modified globin transgenes through insulated self-inactivating (SIN) lentivirus vectors into erythroid cells. We show efficient transfer and robust mRNA and protein expression by the BGT158 vector, and virus titer improvements mediated by the modified intron 2 in the presence of an LCR cassette composed of 5′HS2-4. Our results have important implications for the mechanism of LCR activity at ectopic integration sites. The modified transgenes are the first to transfer intronic elements that potentiate LCR activity and are designed to facilitate correction of hemoglobinopathies using single copy vectors.

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