No abstract

No abstract

We exchanged specific amino acids in the basic region of the murine N-Myc protein and tested the mutant proteins for their DNA binding specificity. The amino acids we exchanged were chosen in analogy to residues of the homologous basic regions of bHLH and bZIP proteins. Mutant N-Myc peptides were expressed in Escherichia coli and specific DNA binding was monitored by gel shift experiments. For this we used palindromic target sequences with systematic base pair exchanges. Several mutants with altered DNA binding specificity were identified. Amino acid exchanges of residues -14 or -10 of the basic region lead to specificity changes (we define leucine 402 of N-Myc as +1; comparable to GCN4 see (1)). The palindromic N-Myc recognition sequence 5'CACGTG is no longer recognized by the mutant proteins, but DNA fragments with symmetrical exchanges of the target sequence are. Exchanges at position -15 broaden the binding specificity. These data were used to build a computer based model of the putative interactions of the N-Myc basic DNA binding region with its target sequence.

Abstract:Novel characteristics of genes identified in the genome of a hyper-thermophilic archaebacterium, Pyrococcus sp. OT3, are described by correlating the 1.74 M bases in the circular genome to the 12 hours in a clock. From 0:00 to 7:00 the bases are used to code more for the germs whose transcription takes place in the clockwise direction, while from 7:00 to 12:00 to code more for the genes whose transcription takes place in the anti-clockwise direction. Genes that are closely related to known eubacterial genes distribute equally through the genome without showing any strong position-preference. In contrast, genes that are closely related to known eukaryotic genes have tendency to cluster from 1:30 to 3:30. On the basis of these findings a possible link between transcription and replication and the origin of archaebacterial genomes are discussed.