RESUMEN
The Drosophila melanogaster gene Sgs-1 belongs to the secretion protein genes, which are coordinately expressed in salivary glands of third instar larvae. Earlier analysis had implied that Sgs-1 is located at the 25B2-3 puff. We cloned Sgs-1 from a YAC covering 25B2-3. Despite using a variety of vectors and Escherichia coli strains, subcloning from the YAC led to deletions within the Sgs-1 coding region. Analysis of clonable and unclonable sequences revealed that Sgs-1 mainly consists of 48-bp tandem repeats encoding a threonine-rich protein. The Sgs-1 inserts from single lambda clones are heterogeneous in length, indicating that repeats are eliminated. By analyzing the expression of Sgs-1/lacZ fusions in transgenic flies, cis-regulatory elements of Sgs-1 were mapped to lie within 1 kb upstream of the transcriptional start site. Band shift assays revealed binding sites for the transcription factor fork head (FKH) and the factor secretion enhancer binding protein 3 (SEBP3) at positions that are functionally relevant. FKH and SEBP3 have been shown previously to be involved in the regulation of Sgs-3 and Sgs-4. Comparison of the levels of steady state RNA and of the transcription rates for Sgs-1 and Sgs-1/lacZ reporter genes indicates that Sgs-1 RNA is 100-fold more stable than Sgs-1/lacZ RNA. This has implications for the model of how Sgs transcripts accumulate in late third instar larvae.
Asunto(s)
Drosophila melanogaster/genética , Regulación de la Expresión Génica , Proteínas del Pegamento Salivar de Drosophila/genética , Secuencia de Aminoácidos , Animales , Cromosomas Artificiales de Levadura , Clonación Molecular , Elementos de Facilitación Genéticos , Proteínas del Pegamento Salivar de Drosophila/química , Larva , Datos de Secuencia Molecular , Secuencias Repetitivas de Ácidos Nucleicos , Mapeo Restrictivo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Glándulas Salivales/fisiología , Alineación de Secuencia , Eliminación de Secuencia , Homología de Secuencia de Ácido Nucleico , TreoninaRESUMEN
Permeability of the blood-brain barrier is restricted with respect to amino acids involved in neurotransmission. This finding is well-documented in the case of gamma-amino-butyric acid (GABA) and glycine. Aspartic acid, which is also considered to be a transmitter, equally does not cross the blood-brain barrier in the rat with ease. This amino acid is also thought to be a transmitter in the retina. In order to examine the permeability of the blood-retina barrier with respect to aspartic acid, and investigation was undertaken of the effect of asparate on the light-induced sum potential of the retina in the isolated, perfused cat eyeball, a preparation which guarantees intact retinal circulation. The findings were compared with findings in the isolated retina where the substance was brought into direct contact with the retinal neurons. It was found that aspartate crossed the vascular barrier only to a limited extent and with delay. These results support the hypothesis that aspartic acid is involved in the retinal information processing.