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RNA PROCESSING: Apo-B
29 RNA PROCESSING: Apo-B Lyn M. Powell
Uptake of dietary cholesterol and lipid and their transport in mam malian serum is dependent upon apolipoproteins. T h e s e proteins contain hydrophobic domains to interact with the immiscible lipid, and many act as ligands for receptors to clear the lipid and direct dif ferent lipoprotein particles to particular tissues. One of the largest apolipoproteins is apolipoprotein (apo-) B, which is the sole protein component of low-density lipoprotein (LDL). High levels of LDL and, therefore, apo-B are associated with increased risk of coronary artery disease in humans. Two different sizes of apo-B are synthesized in mammals (Kane 1983). T h e larger form, known as apo-BlOO, is produced in the liver and is the form found in LDL. T h e smaller pro tein is called apo-B48 and is approximately half the size of apo-B 100. In humans, Apo-B48 is produced only in the gut and is essential for the uptake of dietary fat. T h e cloning and sequencing of apo-B 100 (Knott et al. 1986; Yang et al. 1986) made it possible to address the question of how these two different-sized forms are produced. ApoBlOO is produced as a 4163-amino-acid protein, 5 1 2 k D , from a 14,121-bp m R N A . There is an identical-sized message in human small intestine, which produces apo-B48. Sequencing of this mes sage showed a single difference that could be responsible for producPCR Protocols: A Guide to Methods and Applications Copyright © 1990 by Academic Press, Inc. All rights of reproduction in any form reserved.
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Uptake of dietary cholesterol and lipid and their transport in mam malian serum is dependent upon apolipoproteins. T h e s e proteins contain hydrophobic domains to interact with the immiscible lipid, and many act as ligands for receptors to clear the lipid and direct dif ferent lipoprotein particles to particular tissues. One of the largest apolipoproteins is apolipoprotein (apo-) B, which is the sole protein component of low-density lipoprotein (LDL). High levels of LDL and, therefore, apo-B are associated with increased risk of coronary artery disease in humans. Two different sizes of apo-B are synthesized in mammals (Kane 1983). T h e larger form, known as apo-BlOO, is produced in the liver and is the form found in LDL. T h e smaller pro tein is called apo-B48 and is approximately half the size of apo-B 100. In humans, Apo-B48 is produced only in the gut and is essential for the uptake of dietary fat. T h e cloning and sequencing of apo-B 100 (Knott et al. 1986; Yang et al. 1986) made it possible to address the question of how these two different-sized forms are produced. ApoBlOO is produced as a 4163-amino-acid protein, 5 1 2 k D , from a 14,121-bp m R N A . There is an identical-sized message in human small intestine, which produces apo-B48. Sequencing of this mes sage showed a single difference that could be responsible for producPCR Protocols: A Guide to Methods and Applications Copyright © 1990 by Academic Press, Inc. All rights of reproduction in any form reserved.
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