The murine immunoglobulin alpha gene expresses multiple transcripts from a unique membrane exon.

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• Immunoglobulin heavy chains exist in membrane-bound (m) and secreted (s) forms.
• These forms have distinct carboxy-terminal sequences encoded by different gene segments.

Purpose of the Study:

• To investigate the DNA structure of the alpha m chain's carboxy-terminal end.
• To examine alpha mRNA expression in B cells.
• To understand the transcriptional control of alpha immunoglobulin expression.

Main Methods:

• DNA sequencing of a BALB/c genomic clone.
• Analysis of alpha mRNA expression in transformed and normal B cells.
• In vitro translation to assess protein size.

Main Results:

• The alpha gene possesses a single membrane exon (alpha M1), unlike other heavy chain genes.
• Three polyadenylation signals generate up to six distinct alpha m mRNAs with varying 3'-untranslated regions.
• The secreted alpha (alpha s) protein is smaller than the membrane-bound alpha (alpha m) protein.

Conclusions:

• The alpha gene's structure and transcriptional complexity are unique.
• Differential control of transcriptional termination likely regulates alpha s and multiple alpha m mRNA expression.