Fine analysis of the chromatin structure of yeast RNA polymerase Ⅱ transcription teminators

In order to study the functional structure of the transcription terminators and the mechanism of temination,a survey of the chromatin structure,including the location of DNase I hypersensitive sites and the nucleosome arrangement,of yeast ADH1 and FLP terminators was made.The results show that there is no relationship between the function of the terminators and the existence of DNase I hypersensitive sites.However,it is found that there is always a nucleosmoe at the immediate upstream of the transcriptional termination sites.As a control,the chromatin structures of the pBR322 DNA fragments on the yeast shutter vectors are also investigated at the same time.The random nucleosome arrangement on the bacterial DNA in yesast agrees with the published reports.A new hypothesis,about the mechanism of transcriptional termination is put forward and the reason of different nucleosome arrengement on the DNAs which are originally from different species in yeast is discussed.

Gene expression profiles of the developing human retina

Retina is a multilayer and highly specialized tissue important in converting light into neural signals. In humans, the critical period for the formation of complex multiplayer structure takes place during embryogenesis be- tween 12 and 28 weeks. The morphologic changes during retinal development in humans have been studied but little is known about the molecular events essential for the formation of the retina. To gain further insights into this process, cDNA microarrays containing 16361 human gene probes were used to measure the gene expression levels in retinas. Of the 16361 genes, 68.7%, 71.4% and 69.7% showed positive hybridiza- tion with cDNAs made from 12—16 week fetal, 22—26 week fetal and adult retinas. A total of 814 genes showed a mini- mum of 3-fold changes between the lowest and highest ex- pression levels among three time points and among them, 106 genes had expression levels with the hybridization intensity above 100 at one or more time points. The clustering analysis suggested that the majority of differentially expressed genes were down-regulated during the retinal development. The differentially expressed genes were further classified accord- ing to functions of known genes, and were ranked in de- creasing order according to frequency: development, differ- entiation, signal transduction, protein synthesis and transla- tion, metabolism, DNA binding and transcription, DNA syn- thesis-repair-recombination, immuno-response, ion channel- transport, cell receptor, cytoskeleton, cell cycle, pro-oncogene, stress and apoptosis related genes. Among these 106 differen- tially expressed genes, 60 are already present in NEI retina cDNA or EST Databank but the remaining 46 genes are ab- sent and thus identified as “function unknown”. To validate gene expression data from the microarray, real-time RT-PCR was performed for 46 “function unknown” genes and 6 known retina specific expression genes, and β-actin was used as internal control. Twenty-seven of these genes showed very similar expression profiles between the microarray and real-time RT-PCR data. In situ hybridization revealed both expression level and cellular distribution of NNAT in retina. Finally, the chromosomal locations of 106 differentially ex- pressed genes were also searched and one of these genes is associated with autosomal dominant cone or cone-rod dys- trophy. The data from present study provide insights into understanding genetic programs during human retinal de- velopment and help identify additional retinal disease genes.