文档介绍：Fine Structure and Analysis of Eukaryotic Genes
Split genes
Multigene families
Functional analysis of eukaryotic genes
Split genes and introns
The mRNA-coding portion of a gene can be split by DNA sequences that do not encode mature mRNA
Exons code for mRNA, introns are segments of genes that do not encode mRNA.
Introns are found in most genes in eukaryotes
Also found in some bacteriophage genes and in some genes in archae
R-loops can reveal introns
Examples of R-loops in mammalian hemoglobin genes
Comparison of cDNA and genomic clone maps can reveal introns,
Types of exons
5’
3’
Start
Stop
Transcription start
Translation
Stop
polyA
5’ untranslated
region
3’ untranslated
region
5’
3’
Protein
coding
region
promoter
GT
AG
GT
AG
GT
AG
GT
AG
Open reading frame
Gene
mRNA
Translation
Initial exon
Internal exon
Internal coding exon
Terminal exon
Finding exons puters
Ab putation
. Genscan:
Uses an explicit, sophisticated model of gene structure, splice site properties, etc to predict pare with genomics and cDNA sequences
BLAST2 alignments between cDNA and genomic sequences
.gov/blast/
Find exons for HBB
Sequence for human beta-globin gene (HBB):
Accession number L48217
Thalassemia variant
Sequence for HBB mRNA
NM_000518
Retrieve those from GenBank at NCBI (or the course website)
.gov
Get the files in FASTA format
Run Genscan and BLAST2 sequences
Genscan analysis of HBB gene
BLAST2: HBB gene vs. cDNA
Score = 275 bits (143), Expect = 1e-71
Identities = 143/143 (100%), Positives = 143/143 (100%)
Query: 167 226
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Sbjct: 1 60
hemoglobin, beta 1 M V H
Query: 227 tgtggggcaaggtgaacgtggatgaag 286
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Sbjct: 61 tgtggggcaaggtgaacgtggatgaag 120
hemoglobin, beta 4 L T P E E K S A V T A L W G K V N V D E
Query: 287 tgggcagg 309
|||||||||||||||||||||||
Sbjct: 121 tgggcagg 143